These are SHAB test bars prepared from two different shipments of the same kaolin (used in porcelain body production). The darker one is markedly more plastic also. This underscores the need to characterize the materials you use in production and maintain an ongoing testing program. This difference is actually easy to deal with: Reduce the Bentonite in the body.
In ceramics, glazes and bodies have a chemistry, a mineralogy and a physical presence. All of these need to be understood to adjust and fix issues.