XLFontMBS.Bold as Boolean

(Read and Write property)

XLFontMBS.Book as XLBookMBS

As a font is only valid with the owning book, we keep a back reference here.
(Read only property)

XLFontMBS.ColorRGB as Color

While ColorValue may return indexed color, this property converts to a Xojo color value.
(Read and Write property)

XLFontMBS.ColorValue as Integer

dim book as XLBookMBS // your book
dim textFont as XLFontMBS = book.addFont()
textFont.size = 8
textFont.ColorValue = XLFontMBS.ColorGray25

If book is in RGB mode, you need to use UnpackColor to get red, green and blue color components or color value from the returned number. If book is not in RGB mode, you receive a color number (see XLFontMBS color constants).
If you set value and book is in RGB mode you can use PackColor function to get a numeric value for a color or color components. If the book is not in RGB mode, you can use color constants in XLFontMBS classes.
(Read and Write property)

XLFontMBS.Handle as Integer

(Read only property)

XLFontMBS.Italic as Boolean

If italic doesn't show, maybe check whether the chosen font supports italic.
(Read and Write property)

XLFontMBS.Name as string

Default name is "Arial".
(Read and Write property)

XLFontMBS.Script as Integer

(Read and Write property)

XLFontMBS.Size as Integer

(Read and Write property)

XLFontMBS.StrikeOut as Boolean

(Read and Write property)

XLFontMBS.Underline as Integer

See Underline* constants.
(Read and Write property)