other wise try like this
LOOPAT messtab.
CALLFUNCTION'FORMAT_MESSAGE'
EXPORTING
id = messtab-msgid
lang = sy-langu
no = messtab-msgnr
v1 = messtab-msgv1
v2 = messtab-msgv2
v3 = messtab-msgv3
v4 = messtab-msgv4
IMPORTING
msg = msg_txt
EXCEPTIONS
not_found = 1
OTHERS = 2.
IF sy-subrc <> 0.
MESSAGEID sy-msgid TYPE sy-msgty NUMBER sy-msgno
WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
ENDIF.
IF messtab-msgtyp EQ'E'.
WRITE:/10 msg_txt COLOR6.
ELSEIF messtab-msgtyp EQ'S'.
WRITE:/10 msg_txt COLOR5.
ELSEIF messtab-msgtyp EQ'W'.
WRITE:/10 msg_txt COLOR3.
ELSE.
WRITE:/10 msg_txt COLOR4.
ENDIF.
CLEAR msg_txt.
ENDLOOP.
ULINE.
REFRESH:it_bdcdata,messtab.
ENDLOOP.