Tried out the 7.0.0.FL.20131023 freshly just now.

It seems the jar files for the Sapphire and Silvertail themes contains the entire contents of slf4j-jdk14.jar

Our project uses the slf4j-log4j12 binding, so SLF4J fails to initialize with this in the error log:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/C:/Users/Magnus/.m2/repository/org/zkoss/theme/sapphire/7.0.0.FL.20131023/sapphire-7.0.0.FL.20131023.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/Users/Magnus/.m2/repository/org/zkoss/theme/silvertail/7.0.0.FL.20131023/silvertail-7.0.0.FL.20131023.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/Users/Magnus/.m2/repository/org/slf4j/slf4j-log4j12/1.6.3/slf4j-log4j12-1.6.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.JDK14LoggerFactory]