I thnk the flowers are almost always white. Some may have a tinge of pink or yellow in them. I have not seen any red though.
Some flowers ( on the 'net) seem to be from 'night blooming cactus' which is quite different from 'night blooming Cereus'. I had a hard time trying to figure that out
, until I saw the pictures of whole plants
. The manager at one of the garden centres I buy from said many still call it cactus and that the demand for it is very poor.
I will check with them next time as to the colour. I assumed mine is white.