I have some boar tusks that were boiled too long and handled roughly. One has split all the way along and the other has chipped the end off.

What is the most suitable resin for this kind of repair and how what would you color it with?

Is that you Joe ?

As you might know, near all pig tusks shot in different country's or climates will split open, in time, some near exploding into tiny fragments (ask me how I know that) I my work it was part of my job to stop that & I filled them with candle wax as soon as they dried after boiling & cleaning none have split since.

The ones of my own that split but not too badly I filled & repaired with two part glue, here I use Araldite Glue.

Regular old Elmer's glue will work. Should have been done before they split.

Epoxy sculpt is what you need its a two part epoxy putty that smooths with water, you can repair the cracks with it nicely.

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Simple clear wood glue - never had a problem with the ones I have filled.....

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All good suggestions above. I am a epoxy guy. You can get dye to color the epoxy too.