I’ve simply zested the peel of blood oranges at flameout in past beers with good results. Just be sure to not go down to the pith. As many as six to eight blood oranges works well. You can also shave off the orange part of the skin without getting any pith and let that soak in vodka during the primary fermentation, then add that vodka to the bottom of your keg before racking on top. Probably best to add a little bit of it and taste continuously so you don’t overpower the flavor.
However, if it’s the color you’re after, then the big expensive can of purée might be the way to go. Vinter’s Reserve or something like that is the brand?