I think the phrase "no F2P company gives a damn about their game" is false. It's a cliche and an over exaggeration. If Riot, for example, doesn't give a damn, there wouldn't be new champions or bug fixes, etc. I agree there are still problems, but that phrase is a fallacy.
Furthermore, I don't know for certain, but do Riot employees get paid by projects or by the hours? Do they have a list of things they have to do and deadlines but still get paid by the hours? If so, then it's simply bump another project down a bit. Comparably to others aspects, the cursor color change is, arguably, one of the easiest things they can do. So similarly to how you (yourself, not the Riot team) could do a simple arithmetic problem before resuming a ten page paper, they (the Riot team now) could simply do this real quick.
However, if they get paid by projects, then I agree with you that it could be costly. On the other hand, according to a couple of quick searches on google (which, I know, isn't exactly credible but just for a rough estimate), there is about 8% of men who are color blind and about 27 Million people play league of legends. If half of that amount is male (there's significantly less female who are colorblind so we'll forget about that), 13 million, and 8% of those people are colorblind, which is about 1 million. Let's say even 1 percent of those people buy rp on a regular basis (er....$100 each? idk man xD), that would mean Riot gets about $1 millions. Surely that would cover the cost of "several thousand" and then some. I know this is a really, really, really, not really, rough estimate but I think you get the idea.