Mine varies too and in particular I get the thinner cum which a less obvious white colour if I have been highly aroused for a long time before finally cumming. This thinner cum also seems to shoot a lot further. On the other hand going longer between ejaculations seems to have the opposite effect, i.e. my cum becomes thicker than normal. I think these varations are quite normal.
On the question of the strength of the white colour being to do with sperm concentration I don't believe it is that simple. if you ejaculate into a glass and leave it for some time, maybe 10 to 20 minutes, you will find cum that started out thick has thinned out and the white colour is not so obvious. The thinning out is normal thing. There are a pair of enzymes one which makes you cum thick as it is ejaculated, the other, with a time delay, makes it thinner again and this is exactly what happens if you leave it in a glass like that. I have seen the suggestion this whole thing it to avoid the cum running out of a woman before her vagina has had a chance to return to its normal tightness and then, once that has happenned, it can thin out to let the sperm swim more freely.
But given the colour is less obvious when it has thinned out and yet the sperm that were there at the start clearly have not gone anywehere, there is more to colour than just sperm concentration. Interestingly the cum left in a glass does, at some point in the thinning out process, look like the thinner cum ejaculated after being aroused for ages, Maybe being aroused for ages is derailing that thicken up/get thinner process is some way?