There are a few guidelines you should follow when creating your course in *Information*:
How to turn on Accessibility Block
There are 8 buttons on the block itself. The 3 buttons on the top row displaying an A control text size:
The final button on the top row saves styles changed by the block. Once you have altered the text size or colour scheme, the button will become active, shown by the blue arrow. When it's active, click to save settings. Once saved, they will persist between pages even when you log out.
The bottom row contains 4 buttons, each displaying a different colour scheme. Clicking any of these buttons will apply that colour scheme to the page. Clicking the button on the far left will reset the scheme to default and clear any saved colour settings.