Breeze blocks are grey concrete formed blocks and are usually much larger than the clay fired coloured bricks (which come in different colours). The blocks will probably need to be rendered afterwards (for waterproofing the shed), so you can always paint this to match your colour scheme. If you need to obtain planning consent, you may find that the planners have a preference on the finish - they may want you to match the existing buildings in that area. I love the look of brick personally but it can look out of place if everything else in the area is say masonry or rendered block. What is your shed constructed from ? Do you know what the finish on the flats is going to be ? (you should be able to find this out from the local authority's planning department)