You need some basic knowledge about color spaces (in short described here
http://en.wikipedia.org/wiki/CIE_1931_color_space
) and a reference camera, supported by Adobe Camera Raw. And some patience (a day or two)
The whole thing is about adjusting 9 parameters to get the same result as with reference camera. Digicam sensor has 3 primary colors, and each is defined by 3 coordinates. In DNG and dcraw, primary colors are defined in XYZ color space which is hard to visualize, so my program also accepts coordinates in xyY space, where xy conforms to first diagram on above page (CIE xy chromaticity diagram), and Y is intensity of a color. Parameters are in this order
Red_x Red_y Red_Y Green_x Green
y Green
Y Blue_x Green
y Green
Y
You need to take a picture of some reference image like Macbeth, displayed on the computer monitor. It's not important how well your monitor is calibrated, since displayed colors are not used as reference, but picture of them taken by reference camera. You need to take a similarly exposed picture, with histogram to the right. In my case, it showed up that with same aperture, I need shorter exposure with A620 set on ISO 50 than with 400D with ISO 100
Then, you develop a raw from both cameras with same setting (exposure, WB, etc)
With Coffin's profile, A620 WB is quite wrong, needing about 6500K and tint about 20 for typical daylight, while 5200K with tint around 0 is expected
Since sensors for digicams are similar, you can start applying a A620_V17.cmd to a DNG (on the prompt, type A620_V17.cmd Yourfile.dng), taken with your camera and see what you get. First, you must set Y parameter in the batch file for red and blue to get correct WB. Increasing absolute value of Y increases red/blue intensity in the developed picture
After setting Y parameters correctly, which will take 5-6 attempts, you should check hue and saturation of all colors and move R, G and B in xy plane accordingly. This will take much longer time, since on every iteration, you need to set WB again. In general, moving a point further from the center of diagram will increase saturation around that color, and moving a point in counterclockwise direction will increase hue
Note that, unlike for sRGB or AdobeRGB, primary colors are lying outside the diagram (except red which is inside)
When/if you are satisfied with the result, you can modify a header file of DNG4PS (in my case ...\hdr\PS_A620.bin) with the same arguments, so newly generated DNGs will have new color matrix