toadstorm
If you're in a situation where the art director says “this thing has to be exactly this shade of magenta!” then you're in for a treat. There's two approaches: the simple hacky way is to fix it in post. Handle your whole color workflow using ACES like you normally would, and then at the end of your comp after you've used OCIO to transform everything into your delivery colorspace (probably sRGB), apply your brand colors / color corrections.

The second approach would be to apply the inverse of your usual color transform to the target color. It's a bit like how you'd apply an inverse gamma curve to an sRGB texture (1/2.2 = 0.4545) in order to linearize a texture for normal rendering. The exact operation here depends on what your input and output spaces are, but generally what you want to do is take your source swatch or texture and convert it FROM your output space (Output - sRGB probably) TO your working space (ACES - ACEScg). This will ensure that what you see is what you get. It does come with the possibility of giving you some very weird color values, though, and this could affect your lighting solution (especially if you're trying to match a very bright color).

malbrecht
Hi,

> when working with exaxt color values?

… “exact color values” and “Aces” don't fit into one context in my world :-) (tongue in cheek). ACES, like all other attempts to agree on something, is a “forced definition”, not something exact. Besides, due to some obscure “640kB will be enough for everyone” philosophy, ACES uses 16bit floating point, limiting (necessary) headroom for floating point rounding errors.

That ranted, a well defined color workflow depends on every device being set up properly: From your monitor's calibration and a matching profile for your display pipeline (your Operating System may apply its own “correction”, so may do your graphic card driver) through your tool (Houdini) to your input data (do you need a “de-gamma” to be applied to get into anything linear?). Without knowing your precise workflow it's hard to tell why exactly you are seeing different colors when turning ONE switch in the whole process.

Marc