There’s a saying among watercolour painters: “If it looks right when it’s wet, it’s wrong.”
It’s a little dramatic, but it makes a good point. Watercolour often looks darker and more intense while wet. As it dries, the colour loses some of that intensity.
As a general guide, the change can be around 20–30%, although it varies between pigments and depends on how much water and pigment you use.
One way I deal with this is to make sure those areas are strong enough in the first wash, rather than assuming I’ll be able to correct everything later.