Do you have any spare tiles? And you'll need some grey and some white wool or string or similar. Lay out the tiles in the same pattern you have done the mirror and use the wool as you would grout. Don't glue anything, just sit it in the gaps between the tiles. This might sound a bit crazy but it gives a good idea of how it will look - without stuffing it up! I think you will find that a dark grey or even black grout will make the colours 'pop'. And one or two black accessories would tie it all together. Good luck!