Noel8876 --
I can get your partway towards a solution to your problem. It is possible to change the cell background color of the rows on the left side of each view, but it is NOT possible to change the background color in any Gantt-related pane, such as the Gantt Chart or Tracking Gantt pane.
To change the cell background color for the task rows in the Gantt Chart view, click the Format tab to display the Format ribbon. In the Format section of the Format ribbon, click the Text Styles button. In the Text Styles dialog, leave the All item selected in the Item to Change pick list. Click the Background Color pick list and select a color that will help you with your dyslexia. Click the OK button.
Keep in mind that repeating this process will only change the cell background colors for the task rows in the Gantt Chart view. I would recommend you repeat this process for other views you use regularly, such as the Resource Sheet view, the Task Usage view, and the Resource Usage view. And keep in mind that these changes only apply to the project you currently have open.
If you find a color that helps with your dyslexia, and you apply it to commonly used views, you can copy these modified views to your Global.mpt file so that the colors will be applied automatically in every NEW project you create. To do this, click File > Info > Organizer. On the RIGHT side of the Organizer dialog, select ONLY the views you modified using the preceding process, and then click the Copy button to copy these modified views to your Global.mpt file. Click the Yes to All button in the confirmation dialog.
Hope this helps.