It is hard to say with these guys, there are so many differing species of them, and many look the same. The color will darken some as they age. Mine I've had for nearly 3.5 years and he went for 2.5" to 5" and has darkened considerably. Of couse they are subject to stress and their color does fade with stress.
If you can get shots of their mouths on the glass that might help identify them, or at least narrow it down some.