Paramesotriton- How do you tell if a tail is going blue?

[benjamin]

I have some Paras, I don't know what species they are yet. An increasing area of the tails of two of the newts is lightening in colour, is this a sign that they're tails are going blue and they're entering the breeding season? So far the lightened area on both newts is a light grayish colour compared to their brown and greenish back grounds.