As a Young Eagle pilot and Chapter Coordinator, I'm delighted to see a young person learning to fly! Don't ever stop, as you'll find that it is one of your bigger accomplishments in life.
I've been flying 30 years with the same problem. My dad figured it out when I was helping put up the Christmas lights and I handed him the wrong color bulb. I have the most common deficiency, red/green. Bright colors are no problem, like stop signs and trees. But, a dull, dark green, brown, blue or purple all look about the same. I HATE those colored dot tests. I just can't believe there are numbers in there. I was taken out on the ramp at a towered airport, and the inspector had arranged with the tower to shoot the light gun at us. I identified the colors OK, so was given a SODA- Statement of Demonstrated Ability. That means not being limited to daylight. (I was flying tonight, in fact.) For a Sport Pilot, no big deal, since you're not allowed to fly at night. But, it sure is cool!
I've being doing some flying lately in a Light Sport called a Falcon LS. A verrrry nice plane. (That's what I was flying tonight.) I'm also looking into being a CFI-LS so I can teach in it. Even though a 172 flies by the same rules of physics as an LSA, when it's time for you to solo, you wouldn't be allowed to do it, as a 172 is over 1320 pounds, the limit for an LSA. As I read FAR 61.313, you could get 15 of your 20 required hours in a 172. You would eventually have to transition to a LSA to solo, do at least 5 hours on your own, and take a checkride. Since you already have 20 hours, you might be able to transition to an LSA quickly and get finished up. But, do consider finishing the Private, too. It's quite a bit more work, but learning the additional skills is fun. You'll fly at night, in a control-tower environment, and in simulated instrument conditions. This allows you more priviliges, and gives you more confidence. If you go the Sport Pilot route, I would suggest continuing to fly with a CFI (as opposed to an instructor with a Light Sport rating) if you do intend to someday finish your Private training.
Good luck and blue skies!
Young Eagles Coordinator
EAA Chapter 91