Default values for custom colors missing

[phaer]

Hello! Thanks for your work on this project :)

Running the READMEs example on one of my notebooks with the current develop branch does not work, as -c seems to be a required parameter now.

$ lines-are-rusty notebook-page.rm -o notebook-page.pdf
Expected 5 colors per layer (black, grey, white, blue, red). Found: 

I've reviewed the last commits diff in https://github.com/ax3l/lines-are-rusty/commit/bc6b33f560147c88ad5970c99a29cecf906693c6, trying to pass values from the Default impl below, but that does not work as well:

$ lines-are-rusty -c "black,#bfbfbf,white,#0062cc,#d90707" notebook-page.rm -o notebook-page.pdf 
Error: Failed to parse lines data

Caused by:
    Unknown color: 4

The error seems to be raised from https://github.com/ax3l/lines-are-rusty/blob/bc6b33f560147c88ad5970c99a29cecf906693c6/src/lib.rs#L123, but I don't yet understand how it's caused.

Is this expected behavior, I am doing something wrong?

[phaer]

The latter error seems to be caused by me using the new-ish yellow highlighting color in the notebook I've tested it with. If I add a color for "4" to the TryFrom implementation, it works! So there's only the missing default value open