Blue tinted IRLED.

Just a guess...

It's the same plastic they use on the receivers to filter out visible light so they don't have to qualify and stock 2 types of plastic.

Blue tinted IR receivers seem to be relatively rare, by far the most common these days is the integrated modules which look almost black in normal incident light but are obviously transparent to IR radiation. But that doesn't necessarily mean your guess is wrong.

The blue might filter out the little bit of visible red you get from some IR LEDS. Not sure why that would be seen as a benefit. Do you see any red from them?

The blue tint is probably less lossy that the black you see on IR photodiodes which needs to filter all but IR.