well at this point, you have about 3 options (in order of hardest to easiest)
1. Beg the creators/modders of eq2map to modify the file to change the color of the white X
2. Change it yourself. the DDS/Graphics Modification Help & Info forum has great info on how to modify the dds files (requires some experience with a graphics program like photoshop or paint shop pro)
3. use the file out of someone elses UI modification. Personally, i would try
FetishMaps v6.3 as Zonx creates some amazing things...and looking at his file, it looks like his is an orange O instead of a white X. Just use his dds file in place of the one delete above, or use his full modification to the map window, your choice.
Hope this helps