When you have a background color and you place a graphic with a transparent background or special effect atop it, it may result in an oddly colored box around the image. There are many reasons why this may happen, but it all boils down to transparency data being misinterpreted.
Raster images with clipping paths, transparent backgrounds, opacity settings less than 100%, use blending modes such as multiply or overlay, or have special effect like shadow or glow, all of these have transparency data. The biggest offenders are drop shadow and glow special effects, as the soft faded edges add raster and transparency data that often collide with other color spaces or graphic formats.
The issue doesn’t always display on screen or at your printer’s RIP preview, and it can be quite costly to find the problem after it’s been printed. Call out any effects and transparent objects to your vendor, and ask them to output a proof to look for any issues or color shifts before running the final project. If the project is large format you can request a proof at a reduced size.
Don’t Mix Your Color Spaces
Working within the same color space is a great way to avoid these issues as it’s usually at the root of the problem. Keep all raster or vector images and colors in your layout within the same color space specified by your vendor, (CMYK or RGB).
Make sure that your document colors are not saved as spot colors, even if they have a formula built in CMYK or RGB they won’t always be handled correctly at your printer’s RIP.
Avoiding PMS spot colors for printed projects isn’t always available as brand identity guidelines may require a color match. If you have a critical Pantone spot color make sure you’re working in the CMYK color space. If your layout is in InDesign, click Transparency Blend Space under the Edit drop down menu and make sure it’s set CMYK. RGB’s blend space does not play nicely with spot colors.
Mixing Raster and Vector Graphics
In some cases the issue is caused by mixing raster images (photos) with vector images. Some special effects like drop shadows and glow, add raster data to the object to create the soft faded edges, even if that object is a vector graphic.
If you find this issue and all of your color spaces match, you could try rebuilding the offending graphics in photoshop including the graphic, special effect and background, eliminating the transparency issue entirely. This isn’t ideal as photoshop files tend to be large and unwieldy when working in large format, but it solves the problem.
The Easiest Fix
Sometimes the special effect just isn’t worth the trouble, if your graphic doesn’t NEED a drop shadow effect to make it more legible, eliminate it. You can always create a hard edge drop shadow by duplicating the graphic, changing its color and offsetting it.
Check with Your Vendor
Your print vendor may have advice or solutions to the problem, if you can’t sort it out, recruit their help.
It bears repeating, call out any effects and transparent objects to your vendor, and ask them to output a proof to look for any issues or color shifts before running the final project. If the project is large format you can request a proof at a reduced size.