We need to write an original article for the keyword "Colour By Number Subtraction". Use context when useful: mention various phrases like "Addition and", "MATHS", "Subtraction Color by Number", "Use this butterfly addition and", "NUMBERBLOCKS", "Addition and Subtraction Color by Number", "This video provides an example of how to use", "See how to use two-". Must be 600-900 words, natural headings, avoid unsupported claims, no mention of AI. Use only safe HTML tags: h2, h3, p, ul, ol, li, strong, em. No markdown fences. So output should be plain HTML with those tags. We need to incorporate the context phrases where appropriate. Ensure 600-900 words. Let's aim ~750 words. Structure: h2 introduction, h2 what is colour by number subtraction, h3 how it works, h3 benefits, h2 using butterfly addition and subtraction, h3 example with video, h2 integrating NUMBERBLOCKS, h2 classroom or home practice, maybe h3 tips, conclusion h2. We must use only allowed tags: h2, h3, p, ul, ol, li, strong, em. So headings only h2/h3. Use paragraphs

. Use lists