Default note colors & patterns

A number of defaults for a note's primary visual attributes change from v5.10.1.

In v5, defaults were:

• $Color: 'dark warm gray'
• $Color2: 'light warm gray'
• $Pattern: [no pattern].

From v5.10.1 there are new defaults:

• $Color: 'warm gray dark'
• $Color2: 'dark warm gray dark'
• $Pattern: 'diagonal'

The default apply to new documentent created using v5.10.1 or later. Existing documents' defaults are unaffected.