Gray-scale　image　recolor　or　computer-assisted　color　restoration　is　a　computer-assisted　process　of　adding　color　in-formation　to　grayscale　photographs,　which　is　crucial　in　perceiving　visual　information　by　humans.　An　important　feature　of　this　technique　is　the　ability　to　restore　the　original　style　of　old　images.　Neural　network-based　black　and　grayscale　image　coloring　technology　is　gradually　becoming　a　prevalent　topic　in　current　research　with　the　development　of　computer　vision　and　data　science.　Models　with　DNN,　CNN,　GAN,　and　DCGAN　were　successively　proposed　in　the　recent　few　years,　indicating　a　fresh-new　hot　spot　of　image　processing.　Several　popular　image　re-coloring　methods　have　been　discussed　in　this　essay,　including　a　review　of　recent　research　and　then　a　detailed　analysis　of　the　current　deployment　method.　Finally,　the　essay　compares　the　existing　application,　demonstrating　several　real-world　examples　and　providing　information　and　statistics　on　how　to　apply　this　technique　to　the　industry.　We　also　summarized　current　limitations　and　future　trends　of　this　research　field　to　provide　an　outlook　for　other　researchers.　　©　2022　IEEE.