Thank you very much @acer, it works!! :-D 

@Kitonum Thank you so much, it was such a big help!

@Kitonum 

This is beautiful! Exactly what I want, Thank you!

Just one more question please; What if I have a more complex-shaped area? 

As an example (still not very complex):

inequal_question_2.mw

Thank you again

This is beautiful! Exactly what I want, thank you!!

Just one more question; what if I have a bit less well-shaped area? 

As an example (still not too complex) :

restart; with(plots); with(plots, implicitplot);

inequal(-30.9900990100*am1+8.200000000*dm2-2.8000000001 < 0, am1 = 0 .. .1, dm2 = 0 .. 1);

inequal_question_2.mw

Thanks again!

@acer 
I uploaded in my previous comment the good file. (and now here kuldeni.mw)
Any suggestion why is it happening, why the coloured part is not just where my condition hold true? or how to fix it? 

@acer  Im sorry. This should be the same

kuldeni.mw

It was quite complex so I reduced my code to be able to upload. kuldeni.mw
I hope it works

@acer  Sorry, I thought I uploaded it. Thanks