Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Happy Color® – Coloring Games
Happy Color® is a relaxing color by number game with over 40,000 FREE high-quality pictures
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.8
3,397,564 ratings · Top 5%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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Combine features and design from your favorite apps.
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What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
What's included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
Preview a sample Build Kit No email needed
Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Happy Color® – Coloring Games: map the core Games workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Regularly update content and introduce seasonal themes.
Assumption to check: Limited variety of images and categories
Validate with people who use this workflow before building.
Hypothesis 2
Provide clearer explanations of benefits for each subscription tier.
Assumption to check: In-app purchases can be confusing
Validate with people who use this workflow before building.
Hypothesis 3
Limit ad frequency or offer a more attractive premium subscription.
Assumption to check: Ads can disrupt the experience
Validate with people who use this workflow before building.
Hypothesis 4
Introduce user galleries or sharing options for completed images.
Assumption to check: No community engagement features
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
Happy Color® is a relaxing color by number game with over 40,000 FREE high-quality pictures. From nature and fashion to iconic Disney scenes and artworks, there’s something for everyone. Color by numbers can reduce stress and help you to unwind. Just tap and color – anytime, anywhere. Reasons to download Happy Color®: FIND PICTURES YOU LOVE Happy Color® now includes a powerful search feature, that helps you explore the world of paint by number. Search, discover, and color the pictures that matter to you, whether it’s your hobbies, passions, or favorite topics. That’s what makes our coloring book so special – everyone can find joy in coloring what they love most. UNIQUE DISNEY CONTENT Happy Color® collaborates with world-renowned studios to bring you unique content. Rediscover unforgettable moments and color some of your favorite characters in iconic scenes from Star Wars, Disney's Beauty and the Beast, The Lion King, Aladdin, Cinderella, Winnie the Pooh, and many more in Happy Color®. NEW POSTCARDS CATEGORY Happy Color® brings you a brand-new category, Postcards—a truly special way to experience paint by number. Color postcards, add a heartfelt note, and share your creations as thoughtful messages to friends and family: a thank you, a wish, or just a warm hello. Turn coloring into a gesture of love and attention. NEW DESIGN & THEMES We’ve refreshed the design of Happy Color® to make it even more enjoyable and easier to use anytime, anywhere. Another nice addition is our 4 atmospheric themes: Milky Mist, Pink Dawn, Calm Water, and Warm Night. Create a cozy space for coloring for adults and make every paint by number session more comfortable for your eyes. COLOR ANYWHERE, ANYTIME No Wi-Fi needed. Play this coloring game at home, on the go, or during a quick break – coloring fun is always just a tap away. COLOR FOR A GOOD CAUSE Happy Color® partners with trusted, high-impact charitable organizations around the world. By coloring special pictures, our users can take part in making a difference and contribute to meaningful causes – you color, we donate. ART MADE BY REAL PEOPLE AND PROFESSIONAL ARTISTS Over 100 talented artists worldwide create hand-drawn pictures exclusively for Happy Color®. Each picture in our coloring book reflects human creativity and care. FREE FOR EVERYONE All 40,000+ pictures are absolutely FREE. We believe everyone deserves access to high-quality, inspiring paint by number content without paying a cent. Give yourself a moment to relax and light up your life with Happy Color®. With Happy Color®, you can be part of a global community of coloring enthusiasts, in a safe space where joy and creativity can be shared. We're constantly working to improve. Share your feedback at: [email protected] Join our community and share your creations: Facebook: https://mobile.facebook.com/happycolorbynumber/ Instagram: https://instagram.com/happycolor_official Terms of Use: https://xflowgames.com/terms-of-use.html Privacy Policy: https://xflowgames.com/privacy-policy.html Happy Color® includes many unique pictures handmade by professional artists, as well as pictures of famous characters, comics, cartoons, etc., owned by well-known studios. © Disney © Disney/Pixar © & ™ Lucasfilm Ltd
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Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
React Native
Expo
Zustand
Axios
React Navigation
Firebase
BUILD KIT DIFFICULTY
Intermediate
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
