ValueError 'unknown colour specifier' occurs when we access
export_icon_to_png(). This error occurs when we change the colour of an
icon in the mailing template, because the value of alpha (opacity) in 'rgba'
is in the range of 0 to 1, but PIL Image support colour opacity range 0 to 255.
This commit converts the opacity value range (0 to 1) to a range (0 to 255)
compatible with the PIL image library when the colour specifier is 'rgba'.
sentry - 3933353285
closesodoo/odoo#121696
X-original-commit: 7e4be89f6c0b2f8b82a207030e8a8cb20d72664f
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>