add checks that color column is six hex characters on ingest

[mbjackson-capp]

Looks like the reason the Metra routes don't appear on the map is that there is, once again, unwanted whitespace in a Metra GTFS file column, so the colors aren't valid 6-character hex strings:

Re-ingest Metra routes so colors are correct. For good software design moving forward, add some checks to ensure that color column is valid and strip() whitespace as needed as part of ingest code.

[mbjackson-capp]

It was only 11 rows so I manually edited in Postico rather than doing re-ingest -- they show up now:

Before code is locked next week, we should still add the check that colors are exactly six characters, i.e. match regex r'[0-9A-F]{6}', try strip() if they aren't, and raise a Warning / possibly replace with a neutral gray if it's still not a valid color