Hi there,
My new and upcoming paint line called INSTAR will be based upon
GW shades (Base, Layer, Technical etc) but having the same consistency regardless of the colour base so mixing base colours and layer paints will not be a problem and since they come pre-thinned means you would have to spend less time mixing in third party thinners (Except for airbrush applications, but even in this case, you would use less thinner than with
GW, Vallejo and Army Painter for example).
Also the dropper applicator on the bottle is really small so dispensing EXACT drops is incredibly easy meaning that you'll get the same colour everytime!
See the initial discussion
here
and two of the most recent reviews here
INSTAR paint review
Quick Instar paint review
Until the time of release however (Mid September - Early Jan 2018), I find you can mix base and layer paints, just the base needs thinning first before mixing. Other than that, there should be no problems.