You might be using terminology that is foreign to most folks. Bring it down a couple of notches with a bit more complete explanation, and you might get better help.
I for one, don't know what ACT is, unless you mean the contact management software, and have no idea what an ASN developer is.
So, I may be the only one unenlightened, but it's possible that we won't know what you are referring to, although we may be able to help point you in the right direction with more complete information.
Okay, I'm wearing the Dork hat today, isn't it pretty?
There is a simple way to create an Adobe Color Table ACT file from an existing image that contains the colors you want to have in the ACT file. First, by whatever way works for you, create an RGB image that contains just the specific colors you want. You could fill rectangular selections with specific colors to create a "checkerboard" containing the colors of interest. The arrangement of the colors in the image doesn't matter. Let's call this image the "donor" image.
To create your custom ACT color table containing those specific colors, load a copy of your RGB "donor" image into Photoshop and convert it to indexed color via Image > Mode > Indexed Color and on the Indexed Color dialog window, select Palette as Adaptive, leave the Color Depth at 8 bits/pixel (256 colors), check the Preview box, and for Dither choose "None" because you don't need any intermediate colors. For Color Matching choose "Best". For your case you probably want to check "Preserve Exact Colors", but you can experiment with that. Your image window will soon show a preview of the conversion of your donor image to this Indexed Color setup. OK to apply the change.
Now you want to save the Color Table from this Indexed Color donor image. Menu-select Image > Mode > Color Table to open the Color Table dialog box with your Custom color table displayed. Hopefully 256 colors will be displayed, all of which come from your "donor" image. If you had less than 256 colors in the donor image, your ACT color table should be filled out to 256 colors with a number of black squares. Click the "Save..." button to open the Save dialog box. Enter a unique name and click Save (the .ACT file extension will be added automatically.) OK the Color Table dialog to close it. That will create an ACT file with the name you gave it, containing the colors derived from your donor image.
The only real time consuming step in this method is creating a donor image that contains just the colors that you want in the ACT file.
-- Burton --
It sounds like you want to create swatches -- those are the .ACO file format.
All of it is documented in the Photohsop SDK.
Does anyone know the data format for an ACT file?