Sounds like you are using a natural colouration?!?
Natural powders (at least CND's) are designed to have the pigmentation of a natural nail plate (which is kind of transparent white). Sounds like that is what you may be using as I know they do have a pretty strong white.
As for the mixing of systems... They may look and even hold up ok... but the real problem lies in the amount of initiator to monomer. If those levels are different (which I would bet my money on they are as most do differ) you will run a substantial risk of overexposure as much of the monomer may not ever fully cure (or rather it could take months for it to fully polymerise).
here is an excerpt from Dougs book:
The Schoon said:
A common reason for sensitivity in clients is mixing product lines. Monomers work best with correct polymer. Never use one brand polymer powder with another brand of monomer!
... snip ...
It is impossible to manufacture a monomer blend that would work with any polymer and with any percentage of initiator. The same is true for polymer powder. None work with all monomers!
I met a woman a couple of weeks ago who after 8 months of going to her tek now experiences the most extreme symptoms of permanent sensitization I have ever witnessed. Her tek happened to be intermixing systems. Sad thing about this case is... the client happens to be a tek herself. This almost put her clean out of business (she now has to work with nitrile gloves to prevent breakout).
Hope this helps all