Color Type does not support "inherit" and does not work without a value

[chadfurman]

Describe the bug
Using the "colorType" validator with an optional attribute causes cannot read property 'match' of undefined errors. Likely due to https://github.com/mjmlio/mjml/blob/master/packages/mjml-core/src/types/color.js#L24

I don't want the color to have a default value, because there is not support for the 'inherit' color property here: https://github.com/mjmlio/mjml/blob/master/packages/mjml-core/src/types/helpers/colors.js and I don't want them to have any of these matching colors or any hex color etc.

To Reproduce
Steps to reproduce the behavior:

1. Create a custom mjml component that uses the color validator on an attribute without a default value
2. Use this component in some MJML rendering code somewhere but don't give the color attribute a value
3. Render it to HTML in the normal way
4. Note the error

Expected behavior
There should be some way of allowing font color to be inherited while still allowing font colors to be specified and providing for validation.

MJML environment (please complete the following information):
Appears in latest source. Found while using mjml 4.7.0

[iRyusa]

Yup you're right !
At least the fix isn't that hard, a small guard in the getValue function should do the trick here. Same for inherit we can safely add it to the color list and it will fix #1955 too 😄

Can you open a PR about this ?

[chadfurman]

PR open: #2317

Any chance we can get this back-ported as 4.7.2?

[iRyusa]

We don't update older version of MJML 4.X is the main release channel, thanks for this PR 👍

[iRyusa]

Now live in 4.10.2 thanks !