Sugarloaf Quandary

Some time after I transplanted some sugarloaf chicories, in four of them the leaves began to be tinged with red (see pictures). At first I thought it was black spot (the stains were much darker then), which is common in my wet garden, but the leaves remained firm, that is, they did not rot. The plants are now forming heads, and I wonder, are they another variety of sugarloaf mistakenly mixed in with the common ones?

( I must say temperatures here are above 18 degrees yet)