Well that is one rule that begs to be broken! I think a matte silver roof would look good....not weird at all. I don't think the house below looks "weird."

Pictures would help...are you planning on getting a new roof or is it staying? If it's staying, is it tile, shingle, metal? And what region is it located?

What wall height and roof pitch would you recommend for a house with a flat roofed portico?

Personally , I think that to give advice , you'd need to supply more information -- what the neighbourhood is like , your favourite colours , the plants in your garden , and the likes . I quite like the colours there , but I'd do the front door , the gutters , the window sills and those cap pieces up the pillar supports in an orange or teal or red or similar to add some Wow and excitement , but thats just me .