In most words which end in an unstressed syllable ending in <our> the pronunciation is simply ə. Here is a list of examples:
ardour colour flavour glamour harbour honour humour labour neighbour odour rumour tumour vapour
However, notice the words contour and detour. These are mostly pronounced ˈkɒntɔː and ˈdiːtɔː these days, although for some people the final vowel is ʊə.