Many thanks - sound advice!
I should have added that I had none of the colours concerned! In the end, I took the photo of the mat to a shop and bought the paints that looked likeliest - which proved to be Amaranth Red and Dark Sand. I realised, too, that hoping to match a 2D mat with a 3D textured base was a bit of a fool's errand. In the end, the key thing was to get sufficient redness in there so that the bases look like the mat 'brought to life' (rather than blending in to it). I think I've managed that, so mission accomplished!