Coloured Moissanite

I wonder if if you lovely folk can help me.

I’ve been asked to make an engagement ring with three Swiss blue topaz. However, as it’s such a low grade stone, virtually everything I’ve seen is so poorly cut that it’s all pale, windowed junk that would not be good enough to set into 950 palladium (the metal of choice for this ring). So I’ve been talking to a gem supplier about stones with a better cut and he is trying to source them for me. However, the lady in question has now said that she fancies one central blue topaz with two “plain” side stones. Her young man’s budget would not stretch to two diamonds, so I’m looking at Moissanite, which he is happy with. The point of this is that I wanted an alternative blue stone in case I can’t get a well cut but still affordable Swiss blue topaz, and one that would sit well between two colourless (“white”) Moissanite. So I googled coloured Moissanite and there is indeed a lovely blue colour available.

My question is: is anyone familiar with the colouring process? Is it integral to the stone and permanent or surface only and therefore temporary and completely unsuitable for engagement rings?

Thank you. I hope someone can help answer this.

Helen Hill