Can dishwashing liquid kill sperm?
No. There is no good alternative to condums with spermacide. If there was condums would not be for sale (as much as men complain about them.) Yes. Dishwashing fluid has a high enough acidity to kill sperm exposed to the air. It is, however, too toxic to use as a spermacide. Also, sperm can not survive for more than an hour outside the body.
Dishwashing liquid is available in stores in a variety of colors. Just buy the color that you want. You can also blend your own colors. For example, add a yellow dishwashing liquid to an orange dishwashing liquid and you can get a yellower shade of orange, if that is what appeals to you. Best of all, you can still wash dishes with it!