I'm looking for a specific yaoi/shounen-ai manga about a pair of high school friends who turn lovers. I believe they had different hair colors, and one of them started noticing the other getting taller and more popular in school.

Sorry, that's not very specific. Remember any other detail?

Most pairs have different hair colors, so you can tell them apart. 🤣

Here's a search for 'yaoi' + 'school life' + category 'Friends Become Lovers'
Hope that helps.