B. grandiflora is an accepted name Arif, but the flowers I think are in a cyme where yours so far look to be single as in "uniflora". Are you getting cymes?
http://bioweb.uwlax.edu/bio203...
Whether or not the type of growing medium affects the colour is another matter, it usually does but in this case the flower colour changes anyway and I imagine heat, sun and or shade would have an effect so it's almost like asking how long is a piece of string.
The above link has several tabs along the top to explore about the plant!
