Do you think the 'reference' colorspace should in a separate section in the profile? This would be similar to the PCS in the icc world. It could be an extra line 'reference: !<ColorSpace> ...' before the colorspaces in the profile. The 'reference' name could be reserved so that colorspace -> reference transforms could work the same.

I can see this working as roles with ROLE_REFERENCE but it really feels like a more central OCIO concept than roles and should be separated.

Also looking at the serialization with to_referance and from_referance, I'm thinking it would be easy to read if it was structured like this? what do you think?

--from--
to_reference: !<GroupTransform>
children:
- !<FileTransform> {src: "", interpolation: unknown}
- !<CineonLogToLinTransform>
max_aim_density: [2.046, 2.046, 2.046]
neg_gamma: [0.6, 0.6, 0.6]
neg_gray_reference: [0.434995, 0.434995, 0.434995]
linear_gray_reference: [0.18, 0.18, 0.18]
from_reference: !<GroupTransform>
children:
- !<ExponentTransform> {value: [1, 1, 1, 1]}
--from--

--to--
reference:
to: !<GroupTransform>
children:
- !<FileTransform> {src: "", interpolation: unknown}
- !<CineonLogToLinTransform>
max_aim_density: [2.046, 2.046, 2.046]
neg_gamma: [0.6, 0.6, 0.6]
neg_gray_reference: [0.434995, 0.434995, 0.434995]
linear_gray_reference: [0.18, 0.18, 0.18]
from: !<GroupTransform>
children:
- !<ExponentTransform> {value: [1, 1, 1, 1]}
--to--

.malcolm