it comes up black, I used the same thing for some cosnmetic mast splits. I use "Brummer" wood filler for any stuff I'm going to varnish over, obtainable from B&Q etc.
Not normally, it's a cellulose based stuff, which almost goes off as your putting it in, you can sand it after a couple of hours, then varnish, it comes in different wood cloours, teak , mahogany etc. If anything it's a little light in colour.