Colour blind?

i was reading Karyn's blog about her being colour challenged.
i think she could be colour blind just that colour blind with certain colours(as in she has difficulty seeing certain colours)e.g. Mark Tan cant differentiate red to green and Kristy Tan coloured her grapes Blue colour
In YC mostly the peeps with surname Tan are colour blind which is
1. Mark Tan Eng Meng
2. Kristy Tan Wei Shian
3.Tan Teck Jhim
BUT me(Paul Tan)=),Tan Hock Seng,Christian Tan,Christle Clare Tan,Christobelle Jane Tan,Christopher John Tan,Jeremiah Tan.