Special Coloring of two 3D Graphics with same values

Question

As you can see in the picture below, I have plotted three different functions. Since two functions (red and blue) have the same value for a certain region (equity > 60), I was wondering how I can make it look more intuitiv for the observer that the values are the same. I was thinking of an pattern in red and blue or something similar.

Answer 1

You could do this for example :

gr00 = Plot3D[x^4, {x, 0, 1}, {y, 0, 1}, MeshFunctions -> {#1 + #2 &},
    Mesh -> 30];
gr01 = Plot3D[0, {x, 0, 1}, {y, 0, 1}, MeshFunctions -> {#1 - #2 &}, 
   MeshShading -> {None, Green}];
Show[gr00, gr01]

There is a lattice in the zone where the curves are considered as "equals".
I don't know what's the "equality" criterion (it depends on the ViewPoint, it is implemented in the 3D rendering engine).

One can play with Opacity[] too :

gr00 = Plot3D[x^4, {x, 0, 1}, {y, 0, 1}, MeshFunctions -> {#1 + #2 &},
    Mesh -> 30, MeshShading -> {Directive[Opacity[0.9], Yellow]}];
gr01 = Plot3D[0, {x, 0, 1}, {y, 0, 1}, MeshFunctions -> {#1 - #2 &}, 
   MeshShading -> {None, Green}];
Show[gr00, gr01]

Answer 2

Following @andre... but don't forget to set the ViewPoint to reveal the overlap of the functions in question:

gr00 = Plot3D[x^4, {x, 0, 1}, {y, 0, 1}, 
   MeshFunctions -> {#1 + #2 &},
   Mesh -> 40,
   MeshShading -> {None, {Opacity[0.5], Red}}];
gr01 = Plot3D[0, {x, 0, 1}, {y, 0, 1}, MeshFunctions -> {#1 - #2 &}, 
   MeshShading -> {None, Green}];
Show[gr00, gr01,
 ViewPoint -> {1.1, -1.5, .3}]