+1

Same here, I'm doing a work around now by "tagging" my collections by including the color in the title, such as "RED - My first collection." However, this method isn't as effective as using actual colors. For instance, while writing my dissertation with Zotero, I've organized my chapters into collections to sort articles and notes accordingly. However, some articles are relevant to multiple chapters. Ideally, I'd assign colors to my chapters (collections), and then color-code paragraphs within the text to match the chapter they belong to. This way, I'd instantly recognize that all paragraphs colored red are part of chapter one, blue paragraphs are for chapter two, and so on. It would be incredibly helpful.

I agree wholeheartedly: color choice for various collections is really becoming a necessity. I color code all my research folders, except it is not possible in Zotero.

Have you tried using coloured emojis?
https://s3.amazonaws.com/zotero.org/images/forums/u265723/1wjz6t2f9yvjg9lfh4bs.png
https://s3.amazonaws.com/zotero.org/images/forums/u265723/ptkychlip7yhrqh7127f.png
https://emojicombos.com/square

You can add more information than the colour by using different geometries of emojis.
And you can also use these emojis as emoji tags that display in your library and on annotations in the Reader:
https://s3.amazonaws.com/zotero.org/images/forums/u265723/qcsjjf2bvn6qtrgugq3c.png
https://s3.amazonaws.com/zotero.org/images/forums/u265723/kbg7bxk7l0553zw3els0.png

If you keep an index in a note, you can then use the search on collections to filter the relevant collections:
https://s3.amazonaws.com/zotero.org/images/forums/u265723/ejak3mxtvn3oquocwwd1.png
https://s3.amazonaws.com/zotero.org/images/forums/u265723/uk8lcypt8pkz5vvmt716.png