I found a reference for Dexron III which should be about the same as any other Dexron.
https://docs.google.com/open?id=1KXo09VmkZg_8tLfUkPIRz3M9RudFoZt3-5-UgFarRpxEleo26sIF9AqxzAQ6
Here's one for hydraulic oil
www.hyvair.com/pdf/hydraulicfluid.pdf
There is volumetric expansion which is proportional to temperature. That fact does not necessarily imply that you can't check it cold, but the marks on the dipstick are calibrated for "operating temperature". There is also a question about how to account for torque converter fill, fill of all the other various works of the transmission, and the oil cooler. These factors don't make it impossible, but might give you confusing results based on conditions other than temperature, if you aren't paying careful attention. Another thing you have to worry about is that the transmission is an irregular shaped volume. So if you want to determine where to put your cold calibration tick marks, you need to account for the shape of the transmission. Approximating it as a cube (simplest calculation) might yield bogus results.
Another thing to note is that filling a large reservoir cold might cause an overflow when it heats up, if you accidentally overfill. There are some anecdotal accounts of this happening, burping trans fluid onto a hot exhaust, and causing a fire. Probably in old motor homes with Chevy TH400 & 454.
Here's an explanation of how to calculate the expansion
Thermal Expansion - Volumetric or Cubic
Here is a more thorough treatment of the subject.
Hydraulic Fluid - Properties
The easiest way, is probably just to make empirical observations based on comparisons of hot vs cold readings, with all other variables fixed*.
* You can't easily fix the amount of entrained air in the fluid, but the difference is probably within the margin of error of measurement precision.