Speckled Sussex are a red columbian with black spangling, THEN a white mottling.
Speckled Sussex are Mottled Red Columbian ( Like the color of RIRs with mottling added)
The black is not spangling, they are called chevrons and technically the Black mottled birds have the black chevrons over the white tips too like the SS, you just cant distinguish them since the birds background is the same color.