Chart Line to change colour

[#1]

Hi,

I can have the following chart:

From 14.00 hours I want the blue line to go white.

I've tried to write the following expression for the Background Colour, but it doesnt change anything.

if (Hour>'14', RGB (255,255,255), RGB(0,123,255))

Any ideas folks?

Thanks.

[#2]

This looked like it would work, but still doesnt