I would like to add FX to my AI traffic, but so far I have only found AI planes done by different repainters, so the colours are not consistent (looks kinda funny to have a row of blue-ish MD11 standing next to pink-ish A310s...)Can anyone give me a hint where to find FX planes for AI that have consistent colours

Do a search for the file "FedExAI.zip". This is a nice compilation of FSPainter and AIAardvark aircraft. There are several flightplans available too, so you can choose which suits you better.