There is chocolate in their somewhere, but a good chocolate is the colour of Plain Chocolate, so this mouse is a million miles away from the chocolate it could be. I am more of a mind to say that It may be a poor cinnamon or agout, as I se its littermates are reds, again very poor in colour. However, they may be from the diffeent genes that we dont have in the UK. Depth of colour is governed by selection for the pigment intensisty modifiers that exist in all mice, to answer what I think your question is, no pairing them together wont, in one generation improve colour, yeras of selection would. One of the parents may of been a good colour, and its partner overided that, only you will know the parents and in that case ,if one parent was of good colour mating the young together may improve the colour.