Yes, you can use blue ink on a check, and many bankers and fraud investigators consider it the better choice over black. Blue and black are the two colors banks are set up to read, and blue carries one extra advantage: because most copiers and printers produce black-and-white output, a blue-ink original is easy to distinguish from a photocopy at a glance.
Why Blue Ink Works
Checks are processed through high-speed scanners and, increasingly, through the camera on your phone. Both need strong contrast between the ink and the check’s background to capture a clean image. Dark blue and black give scanners the contrast they need, which is why the two colors have become the informal industry standard.
Blue also has an anti-fraud edge. If someone runs your check through a standard photocopier, the copy comes out in shades of gray. An original written in blue is visibly different from that copy, which makes forgery and duplication easier to spot. Black ink doesn’t offer that tell.
Ink Colors and Writing Tools to Avoid
Several common choices create real problems once a check reaches the bank.
- Red ink. Many check scanners are configured to filter red out as a background color, so red handwriting can disappear from the digital image. This effect is called dropout, and it can make a check unprocessable.
- Green ink. Green is commonly filtered out by scanning equipment for the same reason, with the same dropout risk.
- Light blue or pastel shades. Very light inks don’t produce enough contrast against the check background and are hard to read in scanned images.
- Pencil. No law specifically bans it, but pencil can be erased and rewritten without a trace. That’s an open door for someone to change the payee or the amount, and banks may refuse to process a check written in pencil.
- Erasable ink pens. Same problem as pencil. The ink is designed to come off, which leaves the check vulnerable to alteration.
When a scanner can’t read the amount, payee, or signature, the check is either rejected outright or pulled aside for manual review. Either way, your payment is delayed.
Pen Choice and Check Washing
Color isn’t the only thing that matters. The pen itself affects how vulnerable your check is to a fraud technique called check washing, where a thief steals a check (often from a mailbox), uses chemicals to dissolve the ink, and rewrites the payee or the amount. The U.S. Postal Inspection Service reported initiating 1,487 mail theft cases in fiscal year 2024, with individual schemes sometimes involving hundreds of thousands of dollars in stolen funds.1U.S. Postal Inspection Service. USPIS Annual Report Fiscal Year 2024
Standard ballpoint pens use dye-based ink that sits on the surface of the paper and comes off relatively easily with common household chemicals. Gel ink pens use pigment-based ink that soaks into the paper fibers and is much harder to remove.2Indiana Cybersecurity Hub. Writing a Check? Using the Right Pen, Avoiding the Mailbox Just the Start to Safe Check Cashing Independent testing has shown gel pens vary in how well they resist chemical washing; pens specifically marketed as non-erasable gel ink or fraud-resistant tend to hold up best.
You can lower the risk further by dropping checks inside a post office rather than leaving them in an unsecured mailbox, and by watching your account for unauthorized transactions.
Mobile Deposits
When you deposit through a banking app, your phone camera takes the place of the bank’s scanner, and image quality gets more fragile. Faint ink, low contrast, or unusual colors are more likely to cause a rejected deposit under variable phone-camera lighting than they would on professional scanning equipment.
Stick with dark blue or black ballpoint ink for both the front of the check and the back endorsement. Place the check on a flat, well-lit surface with a contrasting background when you take the picture. Gel pens, markers, and highlighters can bleed or smear during imaging and are generally discouraged for mobile-deposit endorsements.
Endorsing the Back
Blue or black ink is the right choice on the endorsement line too. Some backs of checks have security patterns printed on them, and a faint signature that blends into the pattern can prevent the bank from verifying the endorsement.
Many banks now require a restrictive endorsement for mobile deposits: writing “For Mobile Deposit Only” along with your account number beneath your signature. That language limits the check to a specific account and helps block anyone else from cashing it if the image is intercepted. Wording varies by institution, so check your bank’s app or deposit agreement for the exact phrase they want.
What Your Deposit Agreement Says About Ink
Your bank’s deposit agreement usually pushes the risk of an unreadable check onto you. Bank of America’s agreement states that you bear the risk of loss if you “use check stock or features that cause critical data to disappear or be obscured upon truncation” or if you make a check out “using a lightly colored ink” that causes critical data to be lost.3Bank of America. Deposit Agreement and Disclosures Commerce Bank’s agreement similarly prohibits checks with “ink or other characteristic that interferes with our or any other bank’s ability to produce a digital image of your check.”4Commerce Bank. Deposit Agreement and Disclosures
In practice, if your ink choice causes a processing failure, the financial consequences fall on you. A check that can’t be imaged may be returned, and returned deposit items often carry a fee. Dark blue or black ink from a pigment-based gel pen keeps you well inside what banks expect and gives your check the best shot at clearing the first time.