If you are on Windows, go to 'C:\Program Files\Calibre2\app\resources\viewer.html'. Look for these two lines:
Code:
<symbol viewBox="0 0 1792 1792" id="icon-caret-right">
...
<symbol viewBox="0 0 1792 1792" id="icon-caret-left">
Now, if you want them blue, this is how:
Code:
<symbol viewBox="0 0 1792 1792" id="icon-caret-right" style="fill: blue">
...
<symbol viewBox="0 0 1792 1792" id="icon-caret-left" style="fill: blue">
Or if you want them gone, like before, just use "fill: transparent".
P.S.: a calibre upgrade will overwrite these changes.