Those are rgb values. So the 0 0 for the first two simply mean no green, no blue. The 255 for red is as red as it can be using the 0 to 255 value range. Change the two zeros to a number above zero and the red will become darker, change all of them to 255 and the guidelines will be rgb black.

Create a rectangle. Pull up the color editor and set it to rgb. Play with the three values. That would be the effect on the guideline colors if set identically.