Red is a very emotion provoking colour- danger, passion, blood - it's an attention grabber. Think of the colour which retailers use on "sale" signs , fire engines , stop signs? It's a hue which you can't ignore.
But, if you add white to it (or in the case of watercolour, more water) it becomes pink - which we associate with babies , little girls , flowers, sunsets...
It's not only an important colour on its own , but for mixing others - red is a vital ingredient of orange ,and also of purple.
These are the reds which I currently have on my palette
Cadmium Red - fiery and opaque , tricky to work with but can make beautiful greys when mixed with cerulean blue.
Alizarin Crimson - this one is a beautiful staining transparent pigment BUT it can fade. It's a great red to use to make darks with, especially a lovely dark purple when mixed with Ultramarine.
Quinacridone red - this is a new favourite of mine . It's transparent , staining and lightfast.
Perylene Scarlet - this is an orange/red , apparently very transparent and makes lovely darks- I'm eagerly waiting for my delivery of this from Daniel Smith , I haven't tried it out yet ,but it sounds interesting.
So, if the greys of winter are getting to you, get out those reds and play.