Is this normal to happen?

[Omar5881]

Sometimes I think of something and say the opposite

For example talking about the colour blue for while but in my mind I am thinking that I am talking about the colour red

It's really annoying actually specially when I am discussing something

[GuyWannaHelp]

Yes, this is quite common. I have followed a bunch of Psychology courses and this is one of the first things we learned.

Your brain remembers things through connections between them. Like you said, red is the opposite of blue in this example. This connection may be there because you play games in which you play as blue (the good guys) and fight the red team (the bad guys).
Such a slip occurs when you are either tired or very excited/passionate about something. In the excitement, your brain mixes up the two and you end up saying the opposite of what you meant. There are many, similar example of this. For instance, when you open a package, and you throw away the content instead of the wrapper.

This is preventable by taking things a bit slower and/or making sure you are well rested. By allowing yourself to think a bit more on things, these slips will not happen as often.

[Omar5881]

Amazing , THANK YOUUUUU

[Mustachekitteh]

That happens to me as well, I end up saying the complete opposite of what I'm thinking.