i3 now has its own screen lock program called i3lock. It can display a static background image and a spiffy ring shaped typing indicator that makes it hard to guess how many characters your password has.
Unfortunately the colors of the typing indicator are hardcoded. ravinrabbid made his own color scheme by editing the source code, but I wanted to take it a bit further. So I grabbed the source code and added some command line options to the program so you can select your typing indicator colors at the command line.
Check out my version here: https://github.com/eBrnd/i3lock-color.
Have a look at README.md in the source directory to see how to use it.
If you call i3lock through a script, you can just set your color scheme there, and if you just want to run it from a command line, try setting an alias.