Colourblindness isn't something I'm afflicted with, although when I'm having a bad day I've been known to wear sunglasses to use to a computer (actually I use prescription filters, but they're a very dark green, so they double as sunglasses).
But, there's a mac programme called Sim Daltonism that, given I work with a range of learners with specific learning difficulties and disabilities I just had to look at. The picture at the top is SL with the commonest form of colourblindness. The picture at the bottom is the same view, taken at the same time. Kind of sobering - even if the main thing it's meant for is to check how well your website works for colourblind users.
