A new node named 'Conditional Attribute Formatting' was added for Transaction templates. This node can be added as a child of the 'Attributes' node, and the purpose is to specify a format to apply to the attributes that match the conditions.
In order to do this, make right-click over Attributes node > Add 'ConditionalAttributeFormatting'.
Then, in the node 'Cond Att. formatting' you need to set the property 'Is Primary Key' as True:
Then, in the Attributes node children define what format to apply to the attributes that match the condition. In this case, set some value to the 'ThemeClass' property: