Real nice bunch of kits you've found, especially those Italeri Ferraris
Wish I got friends like yours
Personally I wouldn't use too bright colors like the mica blue. Some subtle metallic color would suit the convertible. Use google's picture search to look for pics of XJS and you'll get loads of factory correct color combos and choose your favorite from there.
I think dark green (BRG) & tan would look nice on the older type coupe XJS.
-Mikko