If the TV is old and you see picture in shades of grey (black and white) you're probably connected with a composhit cable. Connect your Ps3 with a Scart-RGB one for Playstation (it's the same cable for Ps1/2/3), other than correctly see colors you'll have a huge improvement in overall picture quality over the composite cable.
If your TV has more than one SCART input, connect the SCART-RGB to the input number one (AV1, EXT1, VIDEO1...) 'cause usually RGB signal is only supported on the first input (on AV2 input you'll get a CVBS/composite signal even if you're using a SCART-RGB cable).
I had to do the same as you want but for the opposite (With PAL Ps3 I wanted the games to output at 60hz on a old CRT Tv because in PAL mode they're jerky due to 20% less frames at 50hz). With the help of the forum, I installed HAN and firstly tried editing the Registry (changing 2 or 3 options about video mode/output and console region), then I tried editing the game's PARAM.SFOs, but neither of those methods worked for every game (it worked for less than half of my games).
At last I changed the console region (to North America) accessing the debug menu (I changed the XMB from CEX to DEX with HAN Toolbox, changed region and reverted back to CEX).
This way almost all of my games correctly outputted in NTSC 60hz, not all of them btw, I had to change the PARAM.SFO too on some and even so 2 games out of 54 didn't worked even with console region changed and edited PARAM.SFO (One piece PW (PSN): after booting it kicks me back to the XMB. And First of the North Star Ken's Rage (BD): it give me a error message about video mode).
Obviously I can't play PAL DVDs without reverting back the console region. I agree with the solution
@Coro gived you. Imho is better if you leave the console region to NTSC for having the correct screen refresh and game's frame-rate.