Terran beams are the strongest in the game, they have the longest recharge periods
Vasudan beams are weaker than terrans, but they recharge a lot faster than terran beams
Shivan beams are not the strongest in the game, but they are damn efficient in recharge time and active beam time(which is what makes them extremely formidable.
The colossus does use green beams. I think they were bgreens if i remember correctly. Also noted in some of the tech descriptions of the vasudan sentry guns and the destruction of the knossos. The vasudans tend to leave the high powered weapons work like the meson bomb, sentry guns, etc. to the terrans to design. The colossus is a big vessel, it was a joint venture. Vasudans invented the flak cannon, so they made their contribution there. Terrans had more powerful beams, as i'm sure one of the aspects of the colossus was strength(they could have mounted more powerful beams like bfgreen or something). And with strength and what the colossus was designed for (wiping out vessels smaller than it). The colossus doesn't need to worry about refire speed, as it has enough beams to combine power with other beams on the warship, or fire off other beams as it sees fit.
None of the species beams sucks. They all work for each species respectively. And terran beams is "not the only thing they have" in that sense at all. Terrans and vasudans have had beams since a little after the great war (close to 32 years), that also means 32 years of weapons development. If you ask me, terran and vasudan beams work great. Another note, terran and vasudan fighters are a great deal more advanced than shivan fighters and bombers. Terran and vasudan warships tend to go along that line as well. Terrans and vasudans have superior fighter/bomber cover and deterrents than shivan vessels. I find shivan ships more approachable if it's me alone than enemy terran ships when i'm ordered to destroy a cruiser or something. Shivans rarely have fighter beams if not only having one or two AAA beams. The only real thing i would say are unique for the shivans is their great capship killing ability. Another detail about the colossus destroying the sath is that, instead of overcharging the beams, why didn't they just do some beam combining on that disabled jugg (or do leap beam leap frogging...one beam fires the next one in line fires next), well you can't ask that question because that mission was sexp'd most likely
Just thought about the monkey alternative as well.
A balled crippled monkey has the steel to rule over the gtva alphaone