i've got a great procedural colour, but need to do some material re-working. how do i convert houdini's rgb values to photoshop so i can get a real white but keep the perfect colour?

Have you tried R/255, G/255, B/255? I'm pretty sure that should match. If it doesn't then it's likely because Houdini gamma corrects to 2.2 for display by default now.

RGB display in photoshop is dependent on the working color space/profile you have selected in your color settings. Depending on what you have selected in there, what you end up seeing for a given set of RGB numbers may be very different that what you see in a non-color manged application. Houdini's assumed color space appears to be sRGB (2.2 gamma, etc.)Therefore, in Photoshop, make sure your working space is set to sRGB. Note: this will not be perfect, because what Photoshop is doing behind the scenes is:

1. Looking up RGB values in the sRGB profile to get L*a*b numbers
2. Looking up L*a*b numbers in the monitor profile (unless you have a calibration and icc profile on hand, that's likely going to be some default set by your operating system) to get RGB values to send to the monitor.

Whereas houdini (sans a LUT table) is:

1. Gamma adjusting the RGB values.
2. Dumping them to the monitor.

Two two different color management systems are doing very different things. Getting them to line up perfectly is not a simple matter.

Matching a customers product color is crucial in photo realistic 3D productions.
This is something SESI should take a look at in my view and offer maybe different ways or using colors (RBG the adobe way or Pantome colors of hex values as well)

Da Costa

AFAIK, studios usually use a LUT in Houdini.