cli: change torchx color to blue and fix for closed stdout

[d4l3k]

Fixes #418.
Fixes #413.

This changes the torchx logo color to blue since the PT orange can be confused with an red error message and fixes a bug where isatty fails due to stdout being closed in strange environments.

Color choices:

• red/orange - too close to error colors
• green - already used by log role/rank prefixes
• purple - clashes with green
• blue - neutral/meta
• cyan - a little too bright (backup if blue is too dark)
• black - no
• brown - ick
• gray - already used for timestamps
• white - user feedback is colors are good :)

Test plan:

[facebook-github-bot]

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[codecov]

Codecov Report

Merging #419 (94c16b0) into main (2d3a981) will decrease coverage by 0.02%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main     #419      +/-   ##
==========================================
- Coverage   94.20%   94.17%   -0.03%     
==========================================
  Files          66       66              
  Lines        3690     3692       +2     
==========================================
+ Hits         3476     3477       +1     
- Misses        214      215       +1     

Impacted Files	Coverage Δ
torchx/cli/colors.py	58.33% <66.66%> (-1.67%)	⬇️
torchx/cli/main.py	93.33% <100.00%> (ø)

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