The lighter region surrounding a sunspot’s dark core is called the penumbra.
A sunspot has two principal visible parts: the central umbra and the surrounding penumbra. The umbra is darkest because its strong, relatively vertical magnetic field suppresses convection most effectively. The penumbra has a more inclined magnetic field and consists of elongated structures called penumbral filaments, so it appears brighter than the umbra but darker than the surrounding photosphere.
Sunspots are not cold holes in the Sun. They are regions where concentrated magnetic fields inhibit the upward movement of hot plasma, lowering the surface temperature enough to create contrast against the photosphere. The umbra is typically about 3,000–4,500 K, while the surrounding photosphere is roughly 5,780 K.
A common mix-up is reversing the two terms: umbra means the darkest core, while penumbra means the lighter outer region. Newly forming small sunspots may begin as pores without a penumbra.