Alternating row styles can be disabled if you set EnableAlternatingRows="false" in the RadGrid ClientSettings. This will prevent the rgAltRow CSS class from being rendered, and rgRow will be used for all rows. However, you can't "invent" alternating row styles for skins, which do not have them, as Office2007, Vista, etc. In this case you can override the skin and add background color styles for the rgAltRow CSS class, according to your preference.
Overriding a skin is simpler than creating a custom skin.
Note that after you add rgAltRow styles with higher specificity, you will override the background styles for hovered and selected rows and as a result, you will need to redefine these styles with higher specificity as well. Here something similar is done:
(you don't need !important in your case, as you will not be overriding inline styles)
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