Color Blindness

For my second blog post, I decided to research color blindness. I have trouble distinguishing between certain shades of brown, purple and grey so I took multiple online tests that supposedly help to detect colorblindness. One of the tests included pictures of numbers that were a different color from the backgrounds. I could easily pick out the numbers when the colors were reds, greens, blues and yellows but I had trouble distinguishing between the grey and purple shades and I could not see any numbers on certain pictures. Color blindness is due in part by the cones in the eyes so it is possible that some of my cones are defective. Either that or I just really don't know my colors.
Here is the link to the color blindness test that I struggled with:
http://colorvisiontesting.com/ishihara.htm