In my times I don't recall such association, so I'm making this up.

It depends a lot of the curriculum, but I'd try something like:

• Literature - purple, due to purple prose. #7F007F.
• Native language, textual comprehension - red; fire, home. #BF0000.
• Any non-native language, including "foreign" ones and government ones - yellow? #BFBF00 fits I guess?
• Maths - black. Mostly because the most important number is zero, so it gets #000000.
• Chemistry - blue because it's a colour that you barely see in nature, #0000BF. (It reminds me copper sulphate.)
• Biology - green, #00BF00.
• Physics - can I get ultraviolet here? If not, probably grey, #7F7F7F.
• Geography - if not going with an earthy hue I'd not take it seriously, so #3F1F00.
• History - rose to remind you that it's always seen with rose-coloured glasses, so #FFAFAF.

Philosophy, computer stuff, civic order, similar: no idea.