Does the different coloured solar system mean anything

On the universal map, the solar systems have different colours. When i first began, it appeared that i couldn't get to a green or blue system without a sigma or tau hyperdrive booster. Now that i have the different booster, I moved to a green system, but I don't notice any difference. Has anybody noticed a difference between colours of solar systems or is it purely a light-year distance restriction?

I have seen a topic about this on the Steam forum and apparently the color coding works as follows:

• Yellow systems = basic difficulty with normal items
• Red systems (sigma upgrade needed) = medium difficulty with rare items
• Green systems (tau upgrade needed) = hard difficulty with higher chance or rare items
• Blue systems (theta upgrade needed) = extreme difficulty with highest chance of rare items

The difficulty has to do with the environments on the planets and space I assume. Never been to another color system myself though...