They looks ace, those Maxmini heads do wonders! As for something missing, right now all differentiating colours are on the minis' waist. Pehaps adding a small detail like a ribbon to the lance, or a symbol to a kneepad could do the trick?Personally I feel they are great just the way they are though ;-)
Many thanks, the heads are great very detailed high quality resin and a great price, they fit Space marines brilliantly. I agree with the obsevation about the differentiating colours, and I intend to use both your suggestions.