Only recently have I discovered a whole raft of new flat-finish grays - some of them Testors colors I'd never seen before, but many of them also new Tamiya spraypaints - virtually doubling the palette of grays available in this form:
Here I've tried to arrange (and number) them in order of decreasing brightness - lower reflectivity - although the appearance is subjective, due to color-sensitivity of the viewer's eye, the camera taking the picture(s) and the lighting conditions at the time. The front row are all called "gray", of one variant or another - however note some of them appear just as bluish or greenish as the three behind, explicitly called "blue" or "green" - per the following:
1: Testors Camouflage Gray (1933)
2: Testors Flat Gull Gray (1930)
3: Testors Flat Dark Aircraft Gray (1226)
4: Tamiya Light Blue (Luftwaffe) (AS-5)
5: Tamiya Light Gray (IJN) (AS-2)
6: Tamiya Light Ghost Gray (AS-26)
7: Tamiya Gray Green (IJN) (AS-29)
8: Testors Light Sea Gray (1926)
9: Tamiya Dark Ghost Gray (AS-25)
10: Tamiya Medium Sea Gray (RAF) (AS-11)
11: Tamiya Neutral Gray (USAAF) (AS-7)
12: Testors Navy Aggressor Gray (1994)
13: Testors Intermediate Blue (1920)
14: Testors Euro I Gray (1988)
15: Testors Gunship Gray (1923)
16: Testors Panzer Gray (1950)
The advent of these lighter- and bluish grays, in particular, are very welcome - and this is far from the entire selection, at least in terms of the Tamiya (blue-) grays.
The Tamiyas are impervious to mineral spirits - typical paint thinners - which will dissolve (especially fresh) Testors paints, enabling a wide range of Testors-over-Tamiya wash effects. Both types are highly soluble (though the two can't be mixed, AFAIK) in lacquer thinner.
Such Tamiya and Testors paints have different strengths and capabilities: the former goes on very fine and thin, and dries very quickly, while the latter both sticks (at least, under masking tape) and can fill surface defects much better. The very near- if not identical color-matches between some of them, open up possibilities for using both types on different parts of the same build, where advantageous.
Meanwhile, the combination of strongly-adhering Testors and finer-coating Tamiya, should make for ideal latex-chipping of the latter, over a base coat of the former.
All in all, a great expansion of the "tool set"!