I've tried Bad Dragon Cum lube, Spunk Lube and Liquid silk. These are the three that jump out at me for looking like cum in colour. As for sensation, looks and feel, the one that most closely resembles the way cum feels and acts, is Bad Dragon Cum Lube. A run down:
BD Cum Lube is very runny. It just runs and trickles everywhere, so it most simulates very liquidy cum, however it is the "Whitest" of the bunch and still looks creamy on the skin, whereas the other two are a little less white. The best part though, for me, was that this lubricant goes stringy. It strings from the fingers in a similar way as cum does....But it doesnt dry sticky! Weird stuff lol In fact, heres my review of it, have a look at my pictures to see what I mean:
http://grittywoman.co.uk/bad-dragon-cum-lube
Downsides....its a biggie, for me anyway....this lube contains parabens :S
Personally, out of the three, I prefer BD cum lube, not just because it most closely looks AND feels like cum, but because it provides an amazingly slick slipperyness which I have not matched with a lot of lubricants yet, but the parabens thing is a big deal for me too...so I have issues with it too.
Spunk Lube is a hybrid, so you need to do a patch test on silicone toys before you use it. It is also thicker than the BD cum lube and doesnt run, so although it is the same colour as cum, its not as runny and kinda gloops like lubricant is expected to gloop....in other words, you can't splash it about in a "Squirting" effect. It just doesn't move in the way you need it to, to closely simulate how cum dribbles. It also contains parabens. (Methylparaben to be exact, as I am reading the bottle here) My review of it if interested:
http://grittywoman.co.uk/2013/05/review-spunk-lube-hybrid.html
Liquid silk, unfortunately is the one I know less about, because it was two years ago I used my last bottle, so this is coming from memory and may be a bit innacurate, but it looks and acts very similar to Spunk Lube.
All three contain parabens, my recommendation for the most realistic: BD cum lube. My recommendation for the most affordable in the UK with a fab guarantee: Liquid Silk, because it is available from Lovehoney. BD lube is only available from the store in the US and unfortunately you have to pay a high postage and even customs fees etc...so yeah! :S