For 6mm scale I don't think there's anything to reproach yourself for.
If you want a less uniform look in the colour of your bases, there's a couple of things you can try.
The first one sounds wacky, but does work. If you dab some patches of bright colours - red, blue, green, yellow - around on the base just after your first basecoat, your later layers of drybrushing (or whatever you use) will cover them, but leave hints of variations in shade, and thus material, to the eye.
Another thing you can do is use an old brush with rough bristles and stipple some different shades over the top of the bases randomly.
These just help to break up large slabs of a single colour and fool the eye into thinking its broken ground.