You can use the Fluid Design templates to create pages with color palettes of your choice. Your template selections will be available in the Pages section of your Canvas course.
Rename your new copy so it's easy to keep track of your pages.
Open your page by clicking on its new name. Click the "Edit" button near the top right to start creating your content. Note that here will be sample content from the template -- delete and replace that! It's just there to serve as an example, but the page is your canvas.