strange behaviour of the symbol's color

[cht33]

I found that the symbol's color is the same as the char next to it. For example, I have these substitutions

{ "ugly": "\\\\left\\[", "pretty": "[" },
{ "ugly": "\\\\tau", "pretty": "τ", "post": "\\b|_" },

The colors will be like that: The first line is latex source code, the second line is the concealed code. Each \tau has different color and the [ is affected by the pink number. Only the first \tau and the ] have the normal text color, maybe because they are follow by whitespace.

However, when I turn on the editor.renderWhitespace(which i usually turn on), everthing looks quite terrible, I can hardlly see the symbols previous to the whitespace!!!

What can I do to set a color for all the symbols? Is this a bug of this extension's color rendering scheme?