The San Francisco 49ers have leaked their new alternate uniforms, which are all black.

The 49ers have never had an alternate uniform in their history.

Alex Boone will skip the San Francisco 49ers' voluntary workouts and he's open to a trade.

Boone is scheduled to make $3.4 million in 2015.

Boone held out of training camp last season and is one of the NFL's better left guards.

Alex Boone previously defended Jim Harbaugh, but his comments this week represented a major departure.

“He does a great job of giving you that spark, that initial boom,” Boone said.  “But after a while, you just want to kick his ass. . . .  He just keeps pushing you, and you’re like, ‘Dude, we got over the mountain.  Stop.  Let go.’  He kind of wore out his welcome. . . .

“I think he just pushed guys too far.  He wanted too much, demanded too much, expected too much.  You know, ‘We gotta go out and do this.  We gotta go out and do this.  We gotta go out and do this.’  And you’d be like, ‘This guy might be clinically insane.  He’s crazy.’ . . .  I think that if you’re stuck in your ways enough, eventually people are just going to say, ‘Listen, we just can’t work with this.’”

Dorial Green-Beckham has had visits this week with the Cincinnati Bengals and San Francisco 49ers.

Green-Beckham has drawn comparisons to Calvin Johnson and Julio Jones, but he's had issues off the field.

Back in 2014, Green-Beckham was dismissed from Missouri after being the subject of a burglary and assault investigation by police in which he allegedly pushed a female down some stairs during the incident. He didn't face charges from the incident but did wind up transferring to Oklahoma, where he spent an entire season on the practice squad before declaring early for the draft.

The 49ers own the 15th overall pick.

Michael Crabtree has agreed to sign with the Oakland Raiders.

Crabtree's production waned last season and he appeared to lose explosion from a 2013 Achilles injury.

Crabtree, 27, was extremely non-committal about returning to the San Francisco 49ers at the end of the season.

Kurt Warner is working with Colin Kaepernick on staying in the pocket and not using his athleticism as a crutch.

“He can’t do all the running,” Warner said, via Matt Maiocco of CSNBayArea.com. “Now he’s got to become more of a pass-first guy and complement with his athleticism. And he’s never been asked to do that before. And so that’s the process that we kind of went through in the couple of months I was working with him.

“Really trying to get his normal to be a quarterback position as opposed to being an athlete — you know, thinking first as a quarterback and staying in a more throw-friendly position longer so he can get through his progressions and he can be comfortable and he can stay accurate, . . . down through his reads. As opposed to looking at one guy and going, ‘OK, now I can create like I’ve done in the past.’ So that’s the kind of the process we went through.”

Warner spent 10 sessions working with Kaepernick in Arizona this offseason.

Michael Crabtree will visit the Oakland Raiders next week as he continues his free agency process.

Crabtree has also visited the Miami Dolphins.

Crabtree has found his market to be soft this offseason. The San Francisco 49ers have interest in re-signing Crabtree.

Colin Kaepernick, who received a $12.3 million signing bonus last June when he signed a contract extension with the 49ers, is now guaranteed his entire 2015 base salary.

Kaepernick’s $10.4 million base salary for the upcoming season became fully guaranteed on Wednesday as he remains on the team’s roster.

Kaepernick can earn a total of $12.8 million, including a $400,000 workout bonus and $2 million in roster bonuses – or $125,000 for every regular-season game in which he is active.