Yep, yellow extractors and a red rocker cover will look like a Ronald Macdonald engine.
If you really want to paint your extractors just to make them look respectable instead of rusted and ugly then you can buy a flameproof coating made by VHT
http://www.speco.com.au/vht_flameproof.html I've never used it, but I know a few people that have and it is still OK after a couple of years. Please, please, please don't paint them in a bright colour, it'll look crap, go for grey or black.
IF your prepared to spend a bit more (to get a better, more beneficial finish) then do what dVsU12 suggested and get them ceramic coated by HPC.