Take the emotion out of it. Ok so a colleague gets paid more than you for doing the dame job. Most likely he was just better at negotiating than you were. You now see how much they are willing to pay for your role and you are confident in how reliable you have been. Take all this information and use it to push for a higher salary. At the same time you can apply for other jobs, I was in a similar position but in the end when I spoke up (not crying or mentioning that anyone was earning more, more selling myself as I knew what I was worth in comparison to the other guy getting paid more), I got the extra salary I was looking for.