Am I color blind?

I don't see the 6 in the top right image. I took the ishihara test, along with multiple other online color blind tests and all of them say that I'm not colorblind. How can I learn more about this? Please help.

I don't see the 6 in the top right image. I took the ishihara test, along with multiple other online color blind tests and all of them say that I'm not colorblind. How can I learn more about this? Please help.