Is there any way to change the size and the color of letters in arcade announcements?

Yes there is, in the ACP -> Arcade -> Main Settings -> Announcement

 

This is what I have. It's not like yours

You will probably need to go to ACP->Customization->Toolbars and edit the Small/Medium/Large Toolbars and add the buttons that you need.

 

I'm not crazy about it, but really no other way around it.

I did what you told but without any result. I may do something wrong

 

You need to pick the size of the toolbar (Large/Medium/Small) and then you need to drag the buttons from below the box into the toolbar area of the editor box.

I did it. Thank you