One of my friends at work had seen my previous paintings and asked me to do one for her office. Since I was in need of inspiration for a painting, this worked out well. She had mentioned that one of the walls had purple, so I went with that theme.
For the purple, I wanted it all to be in the same "color family" (don't know if that's right term for it). So, I bought a dark purple, and for the different shades, just kept adding white paint to lighten it up.
I was going to make the lines gray (one of the other colors in the office), but after painting every canvas entirely gray (as is my custom for colored lines), and after I put the purple on, I really didn't like the shade of gray. I thought it was too "green". So, I debated between 3 choices: find a different gray, paint the lines white, or paint the lines black.
When painting lines after the fact, I prefer to use acrylics, since they won't bleed as much, and it's easier to do. I can use a painting knife for it, after the tape is set up, so it's quite easy. Since I was going to have to use acrylics, I didn't want to go with gray, since I would have to mix the color, and judging how much to mix, so that everything is the same color, can be tricky. I was afraid that white wouldn't do an adequate hide, so black was the easy choice.
Overall, I'm pretty happy with how it turned out.