Is it true that babies with colic are more easygoing later?

No. I have not heard this, nor is it my professional or personal experience.
No. There is no future predictions of behavior based upon " colicky " behavior. There can be multiple correctible causes of such behavior such as formula intolerance, reflux and such. Peronality is, i think, genetic predisposition modified tremendously by environment. Thus colic may be a factor, but it is not written in stone.
Colic. Colic is such a painful and stressful time for parents, that when it does ease off, it is like a miracle. I would say that they are downright angelic when the colic ends and peace flows back into the household. As to the future: How you interact with your child is one of the biggest factors in his/her "easygoingness," no matter what his/her temperament is. Best of luck.
No. Colic should be a diagnosis made only after other problems have been ruled out. Babies can be fussy due to reflux, food allergies, etc.. Unfortunately, colic is not a predictor of future personality. However, on a positive note, it is also not a guarantee your child will always be difficult.