When I try to pass this code to Lightning CSS:

b {
    color: rgb(max(1, 255), 0, 0);
}

the output is:

/* ERROR: unreachable executed */

but I am expecting that output:

b{color:red}

It looks like the error is at that line of code.

I do not see the point of creating a percentage here, it is just a unit-less value that corresponds to a color channel.