> I remember seeing this game in arcades a lot of time back then and I don't rememeber > the red color too, but now I'm doubting about those memories!
Your memories may be correct. Instead of 0v means black, Monitors should look for a reference signal at some point during the vblank, but the cps1 board doesn't output black all the time during vblank.
Different monitors will look for the reference voltage at different times. So it may coincide with the game outputting red or black. Whatever it thinks the reference voltage is will be subtracted from the voltages during the display.
We don't know what monitors the developers had, it's possible they had a mixture and maybe different people on the team would expect it to look different depending on which monitor they had. Some monitors may not even look for a reference voltage at all and assume 0v
Whoever decided to make the background red may have even known what effect it had and done it on purpose to remove the red from the rest of the screen, but other people involved with development may not be aware of that.
You can modify the hardware to force it to output black during blanking, but who knows whether it's correct to display red or not.