A few years ago some of the big brands had a range of garden paints which were suitable for walls, wood and pots and there were some great deep colours. I went looking for them this year but they seem to have been discontinued, in B&Q there were a few of their own brand but in quite bland colours. Is the wall in a reasonably sheltered location and not prone to the elements? if its ok I'd chance a regular emulsion paint in a colour you like. It may sound like strange advice but I'd water the emulsion quite a lot and apply with a wide brush like the ones they sell for painting fencing / sheds. Its easier to apply to an untreated wall when its thinner and the deeper colours actually cover better. I have done other walls with Masonry paint and found it harder to apply and actually flaked quicker than the thinner garden paint.