like someone said if you have a class 2 , class 1 shouldnt be a problem, apparently the most common reason people fail is due to eyesight, so if your eyes are fine you should be ok.
The ishihara plate test itself aren't a lot more in depth and should be no problem at all for you.
I passed my class 1 med a few weeks back and it really is not as bad as some people make out.
Good luck mate.