Comet C/2017 O1 (ASASSN) was discovered on July 19 displaying already a large diffuse gas coma in the following days.  This color image was taken by Rolando Ligustri on July 27, the green color of the coma is due to the presence of strong C2 emission bands in the spectrum.

Here you can find a preliminary Af[rho] plot of 168P/Hergenrother, referring to its recent outburst:

http://tinyurl.com/8wdmmue