As mentioned in previous posts one of my favorite mediums to work in is Dr Martin's Concentrated Watercolours. I was introduced to these in one of my illustration classes in college and have loved using them ever since.
Dr. Martins are sold in sets of various colors, but I always found it easier just to use primary colors and mix everything. Using Scarlet Red, Lemon Yellow, and True Blue, I can pretty much create any color I need and it has taught me tons about color theory along the way.
Here's some more examples of pieces I've done in that medium. The thing I love about them is the fluidity of them and some of the weird effects you can do.....here's one of the first pieces I did with them.
Here's some more pieces from over the years of various styles but all in Dr. Martins (and Microns and Bombay black ink for lines in some cases)
and my most recent piece that I just did the other day......
For my highlights I either do one of three things. 1. If I can plan far enough ahead, use masking masking fluid to brush over where my highlights would be, paint over it and then peel up when I'm done leaving the white of the untouched surface. 2. Depending on the surface I'm painting on going in with bleach and a brush and "painting" in my highlights. This doesn't seem work on watercolor paper (probably because of the absorption ), but seems to work really well on different kinds of illustration board. 3. Just use titanium white paint and paint my highlights in.
p.s. Be sure and get a UV fixative spray. One of the things about Dr. Martin's is they fade pretty quickly if left in direct light or sunlight unsprayed. But fixing them and if you get them framed putting them under UV glass helps protect them. As a precaution, If a piece is small enough, I make sure to scan them as soon as they are sprayed and if I think I might want to make prints down the road.