I believe I've found an algorithm working in generic case, including partially hidden parts etc. And the result is close to what TLG prints, see below.
The algorithm:
1. add two special colors to ldconfig.ldr: HLwhite and HLyellow - with edge colors white, resp. yellow
2. make older parts HLwhite and parts of the last step HLyellow, make a picture of this "HL model"
3. in your 2D graphics editor (like gimp):
3a. separate (select) yellow colors - ldgview always uses many shades according to model lighting, you need to select all of them together
3b. fill this selected area with (one) yellow and the rest with white
3c. run "Edge detect" filter
3d. make white area 100% transparent
4. use this picture as an overlay of the original model picture
5. thank people in this thread for great conversation and for their enthusiasm
The algorithm:
1. add two special colors to ldconfig.ldr: HLwhite and HLyellow - with edge colors white, resp. yellow
2. make older parts HLwhite and parts of the last step HLyellow, make a picture of this "HL model"
3. in your 2D graphics editor (like gimp):
3a. separate (select) yellow colors - ldgview always uses many shades according to model lighting, you need to select all of them together
3b. fill this selected area with (one) yellow and the rest with white
3c. run "Edge detect" filter
3d. make white area 100% transparent
4. use this picture as an overlay of the original model picture
5. thank people in this thread for great conversation and for their enthusiasm