Pigment changes - WHY?

[Martin Witchard (Cat)]

When I look at a flower bud as it opens I can get a general idea of the colour 
of the final flower. 

In some cases though the flower ends up being considerably lighter/paler 
once opened or considerably stronger/more intense once opened.

How is this explained in light of current knowledge of plant 'pigments'?

For example, a deep red rose opens and soon fades (in a day or two) to its 
'natural' colour of pink. Or a pink budded rose opens pink then becomes 
white in a few days. Or an orange Geum increase its intensity of colour on a 
bright, sunny day (this last may be merely perception and not 
biochemistry).

I'd like to know WHAT 'pigments' are present and WHAT is happening to 
them.  In the pink rose are the 'pigments' photodegraded? Is the same 
occurring in the red rose, and if so, why doesn't it become white? Is it 
possible that the Geum 'pigment' actually intensifies with 
photostimulation?

Answers please if you have them to offer (a good reference would also be 
appreciated!) :)

Thanks,

-- 

Martin