Previously, rainy 05 and wavy 06 had a bottom color with a hard edge.
This means that in order to not have a harsh color transition in the
section, the user would have to match the bottom color to the background
color of the section or vice versa. This commit makes it so that this
color is transparent by default instead. This means that the user can
now simply choose the background color and have the same result, without
having to configure two separate colors.
Part of: odoo/odoo#58333closesodoo/odoo#59420
X-original-commit: 8e6728f7fa486e264737ce068f637c8a76fdb7d9
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>