simpleType  RGB-color  
version  
namespace http://www.w3.org/1998/Math/MathML
type restriction of xsd:string 
source <xsd:simpleType  name="RGB-color">
<xsd:restriction  base="xs:string">
<xsd:pattern  value="#(([0-9]|[a-f]){3}|([0-9]|[a-f]){6})">
</xsd:pattern>
</xsd:restriction>
</xsd:simpleType>