Use following code from your main form Load event, note that if style is changed using StyleManager these changes must be applied again.

C#:

using DevComponents.DotNetBar.Rendering;
using DevComponents.DotNetBar;
 
private void Form1_Load(object sender, EventArgs e)
{
    // Change mouse over colors for the default ButtonItem color table and the ButtonX color table
    Office2007ColorTable table = ((Office2007Renderer)GlobalManager.Renderer).ColorTable;
 
    // Default ButtonItem Color
    Office2007ButtonItemColorTable bt = table.ButtonItemColors[0];
    bt.MouseOver.TopBackground = new LinearGradientColorTable(Color.Red);
    bt.MouseOver.BottomBackground = new LinearGradientColorTable(Color.Yellow);
    bt.MouseOver.OuterBorder = new LinearGradientColorTable(Color.Green);
    bt.MouseOver.InnerBorder = new LinearGradientColorTable(Color.Gold);
 
    // Change default ButtonX color
    bt = table.ButtonItemColors[Enum.GetName(typeof(eButtonColor), eButtonColor.OrangeWithBackground)];
    bt.MouseOver.TopBackground = new LinearGradientColorTable(Color.Green);
    bt.MouseOver.BottomBackground = new LinearGradientColorTable(Color.Gold);
    bt.MouseOver.OuterBorder = new LinearGradientColorTable(Color.BlueViolet);
    bt.MouseOver.InnerBorder = new LinearGradientColorTable(Color.BurlyWood);
    bt.MouseOver.Text = Color.Red;
}

VB:

Imports DevComponents.DotNetBar.Rendering
Imports DevComponents.DotNetBar
 
Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs)
	' Change mouse over colors for the default ButtonItem color table and the ButtonX color table
	Dim table As Office2007ColorTable = CType(GlobalManager.Renderer, Office2007Renderer).ColorTable
 
	' Default ButtonItem Color
	Dim bt As Office2007ButtonItemColorTable = table.ButtonItemColors(0)
	bt.MouseOver.TopBackground = New LinearGradientColorTable(Color.Red)
	bt.MouseOver.BottomBackground = New LinearGradientColorTable(Color.Yellow)
	bt.MouseOver.OuterBorder = New LinearGradientColorTable(Color.Green)
	bt.MouseOver.InnerBorder = New LinearGradientColorTable(Color.Gold)
 
	' Change default ButtonX color
	bt = table.ButtonItemColors(System.Enum.GetName(GetType(eButtonColor), eButtonColor.OrangeWithBackground))
	bt.MouseOver.TopBackground = New LinearGradientColorTable(Color.Green)
	bt.MouseOver.BottomBackground = New LinearGradientColorTable(Color.Gold)
	bt.MouseOver.OuterBorder = New LinearGradientColorTable(Color.BlueViolet)
	bt.MouseOver.InnerBorder = New LinearGradientColorTable(Color.BurlyWood)
	bt.MouseOver.Text = Color.Red
End Sub