Adjust theme colors

apps/block_scout_web/assets/css/theme/_base_variables.scss

@@ -30,8 +30,8 @@ $grays: map-merge((
 ), $grays);
 
 $blue:    #4786ff !default;
-$indigo:  #5b33a1 !default;
-$purple: #997fdc !default;
+$indigo:  #5b389f !default;
+$purple:  #997fdc !default;
 $pink:    #e83e8c !default;
 $red:     #c74d39 !default;
 $orange:  #ef9a60 !default;

apps/block_scout_web/assets/css/theme/_ethereum_classic_variables.scss

@@ -1,3 +1,3 @@
-$primary:       #1b1b3a;
-$secondary:     #40ed9e;
-$tertiary:      #40ed9e;
+$primary:       #1b1b39;
+$secondary:     #4beba0;
+$tertiary:      #4beba0;

apps/block_scout_web/assets/css/theme/_ethereum_variables.scss

@@ -1,3 +1,3 @@
-$primary:       #12455b;
-$secondary:     #4786cb;
+$primary:       #16465b;
+$secondary:     #5ab3ff;
 $tertiary:      #77a4c5;

apps/block_scout_web/assets/css/theme/_kovan_variables.scss

@@ -1,3 +1,3 @@
-$primary: #1BACA4;
-$secondary: #6435c9;
-$tertiary: #6435c9;
+$primary: #28aca4;
+$secondary: #89edda;
+$tertiary: $purple;

apps/block_scout_web/assets/css/theme/_ropsten_variables.scss

@@ -1,3 +1,3 @@
-$primary:  #24a7fb;
-$secondary: #f4c500;
+$primary:  #2fa8f8;
+$secondary: #a2daff;
 $tertiary:  #006aa7;

apps/block_scout_web/assets/css/theme/_sokol_variables.scss

@@ -1,3 +1,3 @@
-$primary:       #539387;
-$secondary:     #8fc4ea;
+$primary:       #559387;
+$secondary:     #add7cf;
 $tertiary:      #38533d;