The swath of yellow is indicative of some stronger storms possible/likely as the squall line continues east. The red area is a short term area. As the daytime heating lessens, as does instability, the tornado threat should diminish soon after this happens. Additionally, the storms are going linear, therefore decreasing the tornado threat.
There are some spotty pink areas that are for the cells that are currently tornado warned and would otherwise be just red of those cells were not present.