First off, great app. I use it to do color sketches on the subway & love it.
One of my two main wishes is about color. The HLS picker is great for picking a color initially, but not great for adjusting a color. If my brush is loaded with red and I want to add some green to it, I have to do some calculation in my head to figure out how to get that done with the HLS sliders. I could use the RGB sliders and add red, but then if I want to lighten or darken a color I have to do similar calculations, and Green in RGB is kind of unintuitive if you're used to thinking in terms of paint for color.
In Photoshop, I use the Lab color sliders, which very closely models a way of thinking about color that I learned from one of my painting teachers. If it's too blue, add yellow, and vice versa. If it's too green, add red (magenta in Lab). If it's too light darken it. Tweak along these lines until the color is right. If you think in terms of cool & warm, this is an invaluable way to work. (It's worth mentioning that Lab is not great for picking/mixing a color initially. So in Photoshop I use it in combination with the swatch palette or the eyedropper once the piece is far enough along. This is a downside to Lab color, but one that I am happy to deal with- in fact I don't know if I can go back to HLS now).
That being said, I think there could be a better solution than Lab color, though I'm not sure what it would be. Others have mentioned a mixing palette, but I find this to be cumbersome, time consuming, & imprecise as well as taking up lots of screen real estate. Another suggestion was adding a feature where the eye dropper added the sample color to the current color based on pressure. Good, but rather inexact and requires me to have the color on the screen already. Maybe it could pull from the swatches, which would be a great solution but still imprecise since it's based on pressure which is difficult to control for us humans. It would be great if there was some precise, very granular/predictable way to control the amount added.
Perhaps there could be some custom "Lab-esque" sliders, where instead of Green/Magenta and Blue/Yellow there could be user-defined a & b. Not sure how technically feasible that is. Just brainstorming.
I saw someone else suggested XYZ color, which is similar to Lab. I have no practical experience with XYZ, so I don't know how similar they are. Lab is supposed to be closer to human perception though, but I would have to use XYZ in a practical setting to say for sure.
In short: a precise, granular, & predictable way to add a certain amount of a color sample to the current color would be great. If nothing else, plain ol' Lab sliders would make me really happy- precise, granular, & predictable without taking up much screen real estate. The only downside would be mixing the initial color, but I could get around that with the swatches/eyedropper.
Thanks again for a great product at a great price![/i]