Fill Definitions
This is where fills used in the workbook are expressed.
<fills count="1"> <fill> <patternFill patternType="solid"> <fgColor theme="4"/> <bgColor theme="4"/> </patternFill> </fill> </fills>
This fill definition specifies a solid pattern fill, whose color uses a themed color, whose index is "4" in the <clrScheme> collection of the Theme part. A <fill> definition is referenced by index (fillId) from either a <cellXf> or a <cellStyleXf>.
A fill record is referenced by zero-based index, meaning the numerical order in which the fill appears under fills.