I Have 2 gen 3 12 lowrance . One unit has older software and shows the custom color on reefmaster map I made. The other unit has newest software update and will not show the depth color shading. Help please

What does the unit show? Are you talking about "depth highlight" or just "normal" depth colours?

It shows contours not the color depth highliting.

What map style did you export?
Can you see any chart categories on the unit? Are any of those currently hidden?
Do you have a raster background as part of the map?

I have the same problem with my hds 7 gen 2 ever since i put the newest update on it (for a few months now), A workaround is to turn Full view or land only view on and back off then the colour shows up. Cant remember if that is the right name for the setting or not tho something like that. Ice on the lakes so havent done it in a bit. I can dig the HDS out if it will help with troubleshooting the problem if needed. The fix is easy enough to work around so never bothered to bring it up.

just to be clear i get depth lines but no colour, until i do ^

Another thing to try here is a soft reset of your device. There have been some posts in the past about people losing polygons in the map view after updating gen 3 firmware that a soft reset has resolved.

I tried what Baitban said and it worked. I went one further and I downloaded REEFMASTER latest software. I exported a new map with a preset style map and worked no problems. Thanks for the trouble shooting.