Blending white with another color to get a new color as opacity color

mixins.less

.rgba(@attr, @color, @opacity) {
	@c1: #fff;
	@c2: @color;
	@{attr}: rgb((1 - @opacity) * red(@c1) + @opacity * red(@c2), (1 - @opacity) * green(@c1) + @opacity * green(@c2), (1 - @opacity) * blue(@c1) + @opacity * blue(@c2));
}