Good to hear of your success.

Part of the trick to getting a good covering job is the first attachment of each piece of film. When you're first starting to learn to cover, it really is worthwhile to have another pair of hands. If you don't have a way to talk the hand's owner into helping you, then it's good to have a way to hold the model or piece securely. You need to work the iron in one hand and slightly tension the covering with your other hand. You don't have to put it down wrinkle free from the start, but you do need it to be somewhat flat and without big wrinkles.

Sorry to hear about the color changes. That suggests the covering isn't Monokote or Ultracote, or that the iron was too hot. Some brands of covering really won't stand heat.

Since it sounds like you have a way to check the temperature of the iron face, take a look at the recommended heat for whatever covering you're using. Rolls of covering often have instructions that include that information.

When a covering mfg mentions that their covering can be attached at xxx temp and it shrinks at yyy temp, you can use that info to your benefit. Tack the covering along the spar for example at the low temperature. Then the covering won't shift around as you pull it flat and tack along the trailing edge, working from mid-span to tip and from mid-span to the root. Then do along the LE the same. You'll wind up with a decently flat piece of covering tacked in place and with no wrinkles. (or only just a few) Keep the low heat setting and work around all the areas where wood is underneath. Iron down all the solid areas. When the covering is tacked in place with few wrinkles, those solid areas will iron down with only small wrinkles. Now turn the iron up to the recommended shrinking temp and go over the open areas. And then go over the solid areas to shrink that covering. There are wrinkles hidden in covering that wasn't shrunk. The sun will bring them out first time you go fly the new airplane.