So i'm working on a game that is very similar to tron. It is two player with the main goal being to not touch any lines.
I have a counter for each player and their scores, but for some reason, when the blue is supposed to lose, it still gains a point.

Link is to project- https://scratch.mit.edu/projects/194245665/

You are testing for the same 2 colors for each sprite that changes their respective scores. I'd think that the blue bike would look for brown or red and the red brown or blue. That is from a quick look

Clear the trails before they move to their beginning positions

New link https://scratch.mit.edu/projects/193848282/

It's what mstone said. To fix it you can add an if touching color but only the opposite color around the block that actually changes the score. You'll also want to move that up to be the first thing that happens when you crash because they'd no longer be touching that color after you clear the lines and reset to the starting positions.

Like so : https://scratch.mit.edu/projects/194290177/

I'd start by slowing it all down. If I set the move to 2 steps instead of 5 steps it seems to detect no collisions at all so perhaps there is something else going on. If I change pen size to 2 it seems to work better but still shows the problem you indicate.

But the scripts for detecting colour are doing too much. All you need is

forever
if <<(play) = [1]> and <<touching color [#4158af] ?> and <touching color [#4158af] ?>>> then
set [play v] to [0]
change [P1 or P2 v] by [1]
end
end

Your other scripts will raise the pen and clear the screen.

Making those changes seems to fix it for me. Not sure exactly what was happening though.