Not everyone is using PowerPoint for presentations; some use it to produce notices or reports. If you are creating something to put on a wall, you don’t want some hyperlinks to be differently coloured to others. The reason this happens is because you, or someone else, has clicked on the hyperlink at some point.
The colours for hyperlinks are linked to themes. Go to the Design tab, then open up the Variants gallery, click Colors – Customize Colors. The Create New Theme Colors dialog box will be displayed.
From the Followed Hyperlink dropdown, select the same colour as for Hyperlink. Click Save. The colours of your hyperlinks will then remain the same.