Jan,
You should be able to customize this by adding the following to your css file.
.claro .dijitButtonText {
color:#03c;
font-family: Arial, Helvetica, sans-serif
font-weight:bold;
}
.claro td.dijitMenuItemLabel {
color:#03c;
font-family: Arial, Helvetica, sans-serif
font-weight:500;
}