|oil on mdf wood 20x20 cms (available here)|
White carnations in a white vase....colourless? Nooo there's plenty of colour if you really look.
Your eye can be trained to see a whole spectrum of colour in the whites you find in flowers, china, cloth etc.
There are some subtle colour and value changes and then the reflected colour from surrounding objects, but you will also need to mix some beautiful greys to set off the delicate whites.
There is very little actual white in a 'white' painting, and if you use too much you'll get a chalky, opaque result.