You can change (override) default appearance of a title(s) used in Slideshow addon by custom CSS lines.
Here is example code which you can use in your web project:

#sp-page-builder h1.sppb-fullwidth-title {
    color: red;
    font-size: 50px;
    font-weight: 400;
    margin-bottom: 20px;
    text-transform: uppercase;
}

#sp-page-builder h1.sppb-fullwidth-title span { 
color: blue; 
font-weight: 700;
}

As always, basic CSS knowledge is requested to modify above code.

Where to put custom CSS

All custom CSS code should be inserted alternatively in one of three places:

1. "CSS" tab in Page Options
2. Custom CSS field in template settings (in template is based on Helix3)
3. In custom.css file

More information here: joomshaper.com/documentation/helix-framework/helix3#custom-css-header-code