I've tinted my fog lights yellow, but just wondering if they are illegal or not?

No issues with them in the EU/UK, (& they are not checked in the MOT), they usually work well in Fog tinted yellow.

& as long as you are only using them in limited visibility nobody will see them on anyway apart from other drivers also in poor visibility conditions.

Thanks for the answers, I didn't think they would be illegal but I couldn't find a definitive answer anywhere else

They not illegal actually its proven your eye can see better in yellow