toRgbaString method
Output color in rgba format
Implementation
String toRgbaString([String template = 'rgba(%r, %g, %b, %a)']) => template
.replaceAll(RegExp('%[rR]'), red.toString())
.replaceAll(RegExp('%[gG]'), green.toString())
.replaceAll(RegExp('%[bB]'), blue.toString())
.replaceAll(RegExp('%[aA]'), (alpha == null ? 1.0 : alpha).toString());