A lot is going on in this area. The blue regions shine primarily by reflected light from nearby stars. The red and yellow regions shine primarily because of emission from the nebula's atomic and molecular gas. Light from nearby blue stars knocks electrons away from the gas and reflect starlight. The dark regions are caused by dust grains, born in young stellar atmospheres, which effectively block light emitted behind them. This complex is in front Globular Cluster Messier 4 visible on the centre left.
A variety of objects can be seen:The yellowish nebula around Antares is Van der Berg 107: Messier 4 is the bigger globular cluster while NGC 6144 is the smaller one shining at magnitude 9 with a 7.4 arc minutes diameter. The reddish nebula surrounding Sigma Scorpii is Sharpless 2-9. IC 4603 is the bluish reflection nebula at the right of the image.