maybe you can get some info from the DialogSetInfo function help.
seems to be like the syntax used in IS 5.x long ago

- parameters are separated by ';'
- parameter are:
1. name of bitmap(s), separated by ',' (internal like '@10550' or exteranl like 'SRCDIR ^ "bitmap.bmp"' - or it may be [SRCDIR]bitmap.bmp in the version you use ...)
2. '1' if there is a transparent color, '0' if not
3. '1' if there is a frame displayed around the bitmap, '0' if not
4. color of the frame (like '0,128,128' which is default; if not defined, do not write anything between the ;; separators)
5. transparent color (defalt is '255,0,255' )
this is in your case:
1: use internal bitmaps 10550 and 10551 (maybe different resolution?)
2: there is a transparent color
3: paint no frame
4: no frame color defined
5: use a blueish color (a dark cyan) as transparent color
does that make any sense?