[color] Fix crash when hex color parses as int, improve error reporting.

[clydebarrow]

What does this implement/fix?

The current color schema has two problems:

• hex: 800000 causes a config-time crash since the value is parsed as an int:

    if len(value) != 6:
       ^^^^^^^^^^
TypeError: object of type 'EInt' has no len()

• An invalid hex value gives a misleading message:

  - id: kbx_green

    [hex] is an invalid option for [2]. Please check the indentation.
    hex: F800000

due to the use of cv.Any() which is indiscriminate in its error reporting.

This PR fixes both those.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

# Example config.yaml

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.18%. Comparing base (4d8b5ed) to head (28471fa).
Report is 542 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #6707      +/-   ##
==========================================
+ Coverage   53.70%   54.18%   +0.47%     
==========================================
  Files          50       50              
  Lines        9408     9579     +171     
  Branches     1654     1687      +33     
==========================================
+ Hits         5053     5190     +137     
- Misses       4056     4065       +9     
- Partials      299      324      +25     

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