How do you make chromium hydroxide from pure chromium?

react them with NaOH?

Sounds fun!  The easiest way is probably to dissolve the chromium in hydrochloric acid, then neutralize it with potassium or sodium hydroxide.

Chromium should be powdered and then added to a volume of sodium/potassium hydroxide, with gentle heating as the hydroxide solution may bump out if it is under strong heating.

This is not quite as easy as it sounds. Chromium is temperamental about dissolving in acid as it can form a passive oxide coat. This is why the 'metal dissolves in nitric acid' doesn't work. It will dissolve in hydrochloric acid, but this gives chromium(II) not the Cr3+ ions you need to make Cr(OH)3.  
Dissolving it in NaOH gives a chromite, not Cr(OH)3 as another answer suggests.

Chromium metal dissolves in dilute hydrochloric acid to form solutions containing the hydrated Cr(II) ion together with hydrogen gas, H2. In practice, the Cr(II) is present as the complex ion [Cr(OH2)6]2+. Similar results are seen for sulphuric acid but pure samples of chromium may be resistant to attack. Chromium metal does not react with nitric acid, HNO3 and in fact is passivated.

Cr(s) + 2HCl(aq) ? Cr2+(aq) + 2Cl-(aq) + H2(g)

Fortunately Cr2+ is very easily oxidised to Cr3+, a little nitric acid add this stage will do it.
Cr2+(aq) - e- Cr3+(aq)

Now add sodium hydroxide solution to get chromium hydroxide. Even this has its problem as the Cr(OH)3 will dissolve if too much NaOH is added, so add cautiously with stirring until no more precipitate seems to form. Then filter off [using a Buchner funnel, or it takes forever] and wash with distilled water and allow to dry and get your chromium hydroxide.
Cr3+(aq)  + 3OH-(aq)  ---> Cr(OH)3(s)