Is this ripe?

this is my grapefruit that I got from Dee.The fruit was on there when she brought it up this summer.

I've never had one ripen before....

Is this ripe?
How do I know?
From the color?
Or should it be soft?

I also Have 2 oranges that are turning orange,how do I know with them?

I thought I had killed my original grapefruit tree that I've had for 10 years,when I put it out this spring it just started loosing all its leaves,and then just looked dead,I threw it in the compost pile and and a couple of months later noticed little green shoots coming out below the graft.

So I grabbed it and dropped it in the tropical garden and kinda forgot about it.I dug up all the tropicals to go in the house and then when We had a few hard frosts(and snow) I started digging the cannas,well there it was( the old grapefruit) ,still alive and green,I have NO idea what it will be now but I dug it up and its in the GH.

Anyone know what they are grafted to?

Can I graft a peice of my new grapefruit to the old rootstock?

I don't have grapefruit, but with the lemons, limes and oranges, they are ripe when they pull loose easily. Just a gentle tug is all it takes. The lemons also turn from green to yellow, so color is probably an indicator. They take a long time to ripen, mine have been on the plant since back last winter.

With oranges it's good to know the variety because they ripen at different times. Color is not an indicator.

I alway to the tast test if its taste right there ripe if not I drink somthing to get the fowel tast out of my mouth