Certainly. It's easy once you're familiar with using custom CSS in Splunk.
http://www.splunk.com/base/Documentation/latest/Developer/UseCSS
In your app, place an application.css file at $SPLUNK_HOME/etc/apps/<appname>/appserver/static/application.css
and put this in it. Now you get to do the fun part, which is picking the hex colors. One color for the default button and one for the hover state -- I deliberately picked two greys below.
.splButton-primary,
input.searchButton {
background-color:#666666
}
.splButton-primary:hover,
input.searchButton:hover {
background-color:#999999;
}
hehe. Yea you have to set hover too or else splunk's default green hover rule will still apply and then users with a history of epilepsy will have to stay away.
Hover 4tw!
You can use CSS to change the SubmitButton color.
.splButton-primary {
background-color: #FFFFFF;
}
You would place this in application.css or dashboard specific CSS. You may generally use Firebug or a similar tool to discover the classes to manipulate.