SCOTTSDALE, Ariz. — Jon Gray’s hair now flows to his shoulders, he has put on 10 pounds of muscle and he has tweaked his delivery.

Most important, he is adding a curveball to his repertoire.

The 6-foot-4, 245-pound right-hander hasn’t reinvented himself, but he has gone to great lengths to improve. It was imperative that he do so, because the training wheels are coming off in 2016.

“I feel like a real starting pitcher now,” Gray said. “I’m ready to go until I am done for the day, so that’s exciting. I’m ready to go for it.”

After finally making his highly anticipated major-league debut last season, Gray finished 0-2 with a 5.53 ERA in nine starts. Pitching under a tightly controlled innings limit, his performance ranged from dazzling to dismal. But few question the talent of the 24-year-old who was picked third overall in the 2013 draft. Using a potent fastball-slider combination, Gray struck out 8.9 batters per nine innings, a strong indicator that he can miss big-league bats.

“Like most young players, it’s about the level of consistency,” manager Walt Weiss said. “We saw flashes of brilliance from Jon last season. But that’s the next step for every young player, to be able to do it time and time again.”

Gray went back and looked at video of every pitch he threw during his 40 innings. He came away with two conclusions: First, he needed to add a deceptive off-speed pitch to keep hitters honest; second, he must make sure he isn’t tipping his pitches.

“The whole purpose of adding a curveball wasn’t so much to have a big breaking pitch,” Gray said. “Look, I know that at altitude it won’t be as sharp as it is everywhere else. So the real reason for it is the differential in speed. Everything I throw is 84 to 96 (mph). I really wanted something slower, something that I could drop in there or even drop in front of the plate.”

Bullpen coach Darren Holmes, whose curveball helped him succeed as a member of the Rockies’ bullpen from 1993-97, is teaching Gray how to make the pitch work consistently.

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“I throw it in the high 70s, which is what I want,” said Gray, who averages a 93-96 mph fastball, 87 mph slider and 85 mph changeup. “The easiest part for me is getting it to drop on the plate, so I do think it’s going to be a good out pitch if I can harness it. And I would like to be able to throw it for strike one. I would really love to.”

Gray has been working on the curveball for about two months in bullpen sessions. He will give the pitch a test drive when Cactus League games begin March 2.

Gray’s debut season certainly had its peaks and valleys. In his second start, on Aug. 10, he pitched a one-hitter for six innings against the eventual National League champion New York Mets at Citi Field. He struck out five, walked two and departed with a 2-1 lead.

“That game jumps out at me,” Weiss said. “(The Mets) were a playoff team and they were playing very well. They were hot and he went in there and had a dominant performance.”

But in Gray’s final start, on Sept. 21, the Pittsburgh Pirates lambasted him for five runs and nine hits, including two home runs, in 4 innings at Coors Field. After that game, Gray wore a black hoodie during his postgame interview and seemed perplexed by his failure.

“I just can’t find that, whatever it is, to make an adjustment to pitch in this place,” he lamented.

Rather than fret and sulk too long, Gray immediately investigated his performances.

“I think I gave some pitches away with my delivery,” he said. “I could see everything I was throwing, just from watching video. I already had an idea that guys were picking pitches up.”

So he has made some minor adjustments to try to solve the problem.

Gray finished the season with a 2.70 road ERA over 20 innings vs. an 8.27 ERA at home over 20 innings. Those numbers gave rise to fears that Gray would be another pitcher wrecked by baseball’s most hitter-friendly ballpark.

But Gray doesn’t believe that, and neither does his manager.

“We got a very small sample size on the home/road thing,” Weiss said. “I’m not concerned about Johnny being able to pitch at our place. That’s not a concern whatsoever.”

Patrick Saunders: psaunders@denverpost.com or @psaundersdp

Shades of Gray

A statistical look at right-hander Jon Gray’s 2015 season with the Rockies:

Starts: Nine

Innings pitched: 40

Record: 0-2

ERA: 5.53

Road ERA: 2.70

Home ERA: 8.27

Strikeouts per nine innings: 8.9

Walks per nine innings: 3.1

Pitches

Fastball: 63.9 percent, 94.4 mph average

Slider: 19 percent, 86.9 mph average

Changeup: 17.1 percent, 85.3 mph

Source: Fangraphs