For dark backgrounds the button border, slider, text and highlight colors need to be changed, there are two methods:

Method 1:

Modify AnimCube3.js and add the following lines (with colors of your choice) to the init function prior to the call to init2:

buttonBorderColor = "white";
sliderColor = "white";
textColor = "white";
hlColor = "gray";

Method 2:

Use direct access to AnimCube internals to change the colors for the four variables shown above. This does not require any additional modifications to AnimCube and is the method used by this page (view source to see the implementation details).