Nteract: Change indigo color used for links and operators in errors to something more readable

[ptcane]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
I find the indigo colored text used for links in markdown cells and also in some elements of syntax error messages hard to read when using the dark theme.

Describe the solution you'd like
Change this color to something more readable on a dark background, perhaps a lighter blue.

Describe alternatives you've considered
Theme customisation or using the light theme. Custom theme seems overkill here, I assume others encounter this issue too with the dark theme.

Additional context
Add any other context or screenshots about the feature request here.

[willingc]

Thank you for filing an issue @ptcane. Which OS are you using?

[ptcane]

@willingc MacOS.

this could be an issue highlighted by my monitor (which hasn't got very good contrast) but I suggest it's likely to be an issue in part for others too. I've not encountered issues with other alternatives (VSCode, jupyterlab dark theme, etc)

[ptcane]

@willingc also poor visibility on Android phone.

[captainsafia]

Thanks for the feedback!

This issue is related to the fact that our syntax highlighter doesn't update when the theme is switched from light to dark theme.

There's a dupe of this issue somewhere but having trouble digging it up as I'm on mobile.

Tagging this for hacktoberfest since it should be new contributor friendly.