Grayscale to color in Photoshop

[3Deep]

Ok I got a family that's wants to use one color royal blue of all colors for a a black persons picture, I got in grayscale/desaturate, now how do I get that in all blue color...yes I have forgot a step, it's just for them to look at.  If I didn't have to show them I'd be fine LOL

[Frog]

I am no PS wizard, and in fact, still use v7, LOL! I hope that this is what you are talking about.
At any rate, the question intrigued me so I grabbed a pic I had open anyway, mode to grayscale (like I think you said you already did)
Then it was Mode/Duotone (where I then changed Color 1 to some Pantone blue, and it then made a monotone like you see here.
You'll just have to play with what color you use.

btw, check out my uninvited house guest on the Mercedes wheel cover

[UltraSeps]

This is best done as a duotone, using two blues, a light and a dark.  And no, the duotone function built into Photoshop won't pull it off.  I have duotone software that does this (shameless self promo LOL) although you can probably figure it out somehow.  If you'd like to send me the original high-res image, I'll be more than happy to do it.  It'll take all of a few minutes.  From there you can change the colors of the blue channels to specification.

[mimosatexas]

in photoshop go to IMAGE>ADJUSTMENTS>HUE/SATURATION then when the window pops up click COLORIZE in the bottom right.  You can change the hue/saturation to whatever shade of blue you want.

[Full-SpectrumSeparator]

There are many ways to do this in photoshop, here is one easy way showing in the attached image, some other methods would be to use the gradient-map adjustment, or go to multichannel from greyscale or just duplicate a neutral greyscale rgb red, green, or blue channel and change to a spot-color and set to the color you want... set a substrate channel and set the color to have it going over a shirt color you could change.    Do you have the image you are working with and want to see some options, using built-in aspects of photoshop? 

[Gilligan]

There are many ways to do this in photoshop, here is one easy way showing in the attached image, some other methods would be to use the gradient-map adjustment, or go to multichannel from greyscale or just duplicate a neutral greyscale rgb red, green, or blue channel and change to a spot-color and set to the color you want... set a substrate channel and set the color to have it going over a shirt color you could change.    Do you have the image you are working with and want to see some options, using built-in aspects of photoshop?

That's how I would do it... Screen.