I work with Vallejo....no problem, use their thinner.
Model master.........use alcohol or their thinner
Tamaya........use their thinner or as I have read, lacquer thinner which tamaya sells or get at Lowes or Home Depot.
Italeri......doesn't matter what I use.....it's just disagreeable.
In searching for exact fs colors not all brands cover the territory so your forced to search. That being said I find that my main issue then becomes dealing with the particular paint brand that resolves the FS issue but then creates issues of dealing with the paint brand.
My thoughts at this point, frustration considered, is to settle on one or two paint brands and determine how to deal with the FS issue, ( I.E. mix two thirds of this color and 1 third of another color).
I'm beginning to think that given scale issues, fading colors in an aircrafts life, and variations in paint schemes between two or three aircraft in the same squadron at the same time that fs is a relative guide and from a modelers perspective knowing your materials is more important then being precise in color matching.
I think I've come to my conclusion on the issue but I'm interested in what others have to say about dealing with this.
thanks
rbtvgo