In FireMonkey applications, we preset certain properties for each component via the style.
If you want to change the font color, font size etc. at design time for a control such as TButton, you need to select StyledSettings in the Object Inspector and uncheck any of the StyledSettings that you want to manually override.
This allows you to go to the Font property in the Object Inspector and change the font style, size etc. without using the presets applied via the style.
For more information, see: http://docwiki.embarcadero.com/Libraries/XE5/en/FMX.Graphics.ITextSettings.StyledSettings
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