Yes. Transcribed into IPA, those words would be [se] and [sɛj], respectively. The [e] sound sounds something kinda like the "i" in "did," and the [ɛ] sound sounds more like the "e" in "bed." Also «sei» ends with a bit of an "ee" sound or a "y" sound at the end, kinda like in the word "boy." Of course, English does not have great examples of these sounds. Portuguese has these two different "e" sounds; so does French and Catalan, but not Spanish.