I wondered about that. I think merrillianum should be bluer. Correct?
I have both,and as i received them in very very bad conditions years ago,i potted them together(are on a mount potted in a net pot with very large bark...base of the plant stay on the mount and roots go in the bark...)... now after years of growing the difference,as they are in the same mount/pot, is evident!
About flowers...i noticed that the colour of flower is affected by both temperatures and light... and may vary from white/greish to nearly blue depending on conditions....
Without a dissection,the differences in flower at first sight,are very little....but gokusingii seems to have bigger flowers with larger segments and much more substance...
The real difference is in the plant morphology...
C. gokusingii have erect growing,short and stout leaves with paler green colour
C. Merillianum have pendulous habbit,thiner and longer leaves,a more elongated general shape of the plant and deeper green colour...
Somethink i noticed on my plants...that may not be a rule...
In the base of the plant,where old leaves are gone,in C. merillianum the stem becames black in C. gokusingii stay greenish to pale brown...
While established are not difficult plants... and can take a very wide range of temperatures... but C. merillianum is more a shy flowerer if take too low temps and not enough like,while C. gokusingii is more easy flowering...
For example this winther i left plants in very cool conditions (too cool... i was worryed they may die 6-15 for + 4 months) and they passed the winther fine...but now only gokusingii is flowering...(in flower now...)