ok cheers guys so the organs should be the same colour all the way through then?
Not neccesarily.
Kidneys in particular can have a colour variation - lambs kidneys, for example, will have a paler outer than inner and a white/cream 'core' - remove the core as it's pretty tough. Kidneys are also quite soft - if you try frying them whole, unless they're very small, you'll likely overcook the outside and leave the inside quite bloody - quartering them is about right if you want to cook them quickly. Hugh Fluffystockingtops 'Lambs Kidneys with chilli and lentils' recipe is a good one to start out with, let me know if you've not got the River Cottage Cookbook and I'll pass the recipe on.
Liver and heart does tend to be the same colour throughout, although hearts have all sorts of tubes, cavities, connecting tissue and valves in them. The whole thing is quiet edible though, just remove any bits which feel like they'll be too tough to chew. You'll spot the bits which need removing from liver very easily.
Hearts tend to favour a good slow roast full of stuffing unless you like a good chew - with that said I'm quite partial to diced heart flash fried in olive oil, with garlic, chillies and worcester sauce.
As has been said, discard any diseased organs immediately. They do, usually, look very unpleasant and not something you'd want to eat anyway.