I have adjusted my gamma with the black and white gradient image and got the values 0.7, 0.9, 0.8 respectively.
try too boost your gamma to over 2 on each RGB channel.
i had the same, far under 2 colours really awfull with APA102 also with a friend of mine.
my setting now is 2.4 Gamma on each channel, now colours is bursting out of there.
i hope it works.