Why my PCB changes color?

The first pic I took after etching and washing the PCB, it was nicely shining but after drilling and soldering and 2-3 days later my PCB changed it's color(pic 2). there are some bluish spots formed over copper tracks. Why? How to remove it? and how to stop it forming on the other PCBs?

Comments

[steveastrouk]

Its oxidising. Pure copper does it when exposed to the air.

After you make it, either tin plate it, or assemble it quickly and lacquer it with a spray on lacquer - NOT water based.

[lemonie]

I've not seen solder go that colour, is it lead-free or something?

L

[SaurIMX]

That because of camera flash

[steveastrouk]

Didn't notice that - lighting perhaps ?