how to draw interchange & color bordes with much more hardiness?

[sayhello]

hello dear experts - good day dear community, 

i have a question;  how to get more hardiness in the colors - especially where two fields meet each other


in other words - see the example: how to get the image and the border of the two different fields 

a. blue 
b. yellow 

in a better shape - with a harder borderline!?

   


i hope that i was able to describe what is needede!?
if i have to explain more - then lemme know.  i love to do that.. - if necessary.


love to hear from you