Shouldn't be too hard to find plenty contenders for spring and summer colour but in autumn you could try autumn flowering crocuses, the smallest colchicums and Cyclamen cilicium to start with. Cyclamen coum in winter though it can get big after a few years. Others for autumn and winter? My mind has gone totally blank. Earliest crocus for winter is C. laevigatus for me. Looking at my own (winter) troughs at the moment, there's no colour at all except green and grey.
