If the purpose of posting the content is to communicate something about the colors in that image or web page, then it is important to provide some other way of understanding the information.
Reds and greens are often indistinguishable
This is not normally a problem except in cases where the colors convey important information. Under these circumstances you will need to either change the content or graphic or provide an additional means of obtaining the same information. For example, provide an explanation in the text itself.
Color and Alert/Error Messaging
Don’t rely on color to convey critical information such as alerts and error messages. See more info about this under the Alert/Error Messaging section.